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SMT回流焊原理以及工艺 - SMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】
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word-wrap: break-word !important; max-width: 100%; border-top: rgb(255,102,0) 1px dashed; border-right: rgb(255,102,0) 1px dashed; white-space: normal; word-spacing: 0px; border-bottom: rgb(255,102,0) 1px dashed; text-transform: none; color: rgb(62,62,62); padding-bottom: 0px; padding-top: 0px; font: 16px/25px 'Helvetica Neue', Helvetica, 'Hiragino Sans GB', 'Microsoft YaHei', Arial, sans-serif; padding-left: 4px; margin: 0px; border-left: rgb(255,102,0) 1px dashed; widows: 1; letter-spacing: normal; padding-right: 4px; background-color: rgb(255,255,255); text-indent: 0px; -webkit-text-stroke-width: 0px"></section><section style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; color: rgb(62,62,62); padding-bottom: 15px; padding-top: 15px; padding-left: 15px; margin: 3px; line-height: 24px; padding-right: 15px; -webkit-tap-highlight-color: rgba(0, 0, 0, 0); box-shadow: rgb(170, 170, 170) 0px 0px 3px"></section><span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; padding-right: 0px"><span style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; color: rgb(123,12,0); padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px"><strong style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">1、什么是回流焊</strong></span><span style="box-sizing: border-box !important; word-wrap: break-word !important; font-size: 14px; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px"><span style="box-sizing: border-box !important; word-wrap: break-word !important; font-size: 14px; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px"><br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 回流焊是英文Reflow是通过重新熔化预先分配到印制板焊盘上的膏装软钎焊料,实现表面组装元器件焊端或引脚与印制板焊盘之间机械与电气连接的软钎焊。回流焊是将元器件焊接到PCB板材上,回流焊是对表面帖装器件的。回流焊是靠热气流对焊点的作用,胶状的焊剂在一定的高温气流下进行物理反应达到SMD的焊接;之所以叫"回流焊"是因为气体在焊机内循环流动产生高温达到焊接目的。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 回流焊原理分为几个描述:</span></span><span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; padding-right: 0px"> <span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; padding-right: 0px"><span style="box-sizing: border-box !important; word-wrap: break-word !important; font-size: 14px; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px"><img alt="1.jpg" width="600" height="378" src="/d/file/jszc/2017-10-16/0ed8edb3ac8f52437d998a9266f32909.jpg" /></span><span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; padding-right: 0px"><span style="box-sizing: border-box !important; word-wrap: break-word !important; font-size: 14px; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">(回流焊温度曲线图)</span><span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; padding-right: 0px"><span style="box-sizing: border-box !important; word-wrap: break-word !important; font-size: 14px; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px"><br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> A.当PCB进入升温区时,焊膏中的溶剂、气体蒸发掉,同时,焊膏中的助焊剂润湿焊盘、元器件端头和引脚,焊膏软化、塌落、覆盖了焊盘,将焊盘、元器件引脚与氧气隔离。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> B.PCB进入保温区时,使PCB和元器件得到充分的预热,以防PCB突然进入焊接高温区而损坏PCB和元器件。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> C.当PCB进入焊接区时,温度迅速上升使焊膏达到熔化状态,液态焊锡对PCB的焊盘、元器件端头和引脚润湿、扩散、漫流或回流混合形成焊锡接点。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> D.PCB进入冷却区,使焊点凝固此;时完成了回流焊。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <span style="box-sizing: border-box !important; word-wrap: break-word !important; font-size: 16px; max-width: 100%; color: rgb(123,12,0); padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px"><strong style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">双轨回流焊的工作原理</strong></span><br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 双轨回流焊炉通过同时平行处理两个电路板,可使单个双轨炉的产能提高两倍。目前, 电路板制造商仅限于在每个轨道中处理相同或重量相似的电路板。而现在, 拥有独立轨道速度的双轨双速回流焊炉使同时处理两块差异更大的电路板成为现实。首先,我们要了解影响热能从回流炉加热器向电路板传递的主要因素。在通常情况下,如图所示,回流焊炉的风扇推动气体(空气或氮气)经过加热线圈,气体被加热后,通过孔板内的一系列孔口传递到产品上。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> </span><span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; padding-right: 0px"> <span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; padding-right: 0px"> <span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; padding-right: 0px"><img alt="2.jpg" width="600" height="451" src="/d/file/jszc/2017-10-16/69526d64d3ea1196d469227b90845589.jpg" /><br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; padding-right: 0px"><span style="box-sizing: border-box !important; word-wrap: break-word !important; font-size: 14px; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">可用如下方程来描述热能从气流传递到电路板的过程,q = 传递到电路板上的热能; a = 电路板和组件的对流热传递系数; t = 电路板的加热时间; A = 传热表面积 ; ΔT = 对流气体和电路板之间的温度差 我们将电路板相关参数移到公式的一侧,并将回流焊炉参数移到另一侧,可得到如下公式: q = a | t | A | | T<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 双轨回流焊PCB已经相当普及,并在逐渐变得复那时起来,它得以如此普及,主要原因是它给设计者提供了极为良好的弹性空间,从而设计出更为小巧,紧凑的低成本的产品。到今天为止,双轨回流焊板一般都有通过回流焊接上面(元件面),然后通过波峰焊来焊接下面(引脚面)。目前的一个趋势倾向于双轨回流焊回流焊,但是这个工艺制程仍存在一些问题。大板的底部元件可能会在第二次回流焊过程中掉落,或者底部焊接点的部分熔融而造成焊点的可靠性问题。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <span style="box-sizing: border-box !important; word-wrap: break-word !important; font-size: 16px; max-width: 100%; color: rgb(122,68,66); padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px"><strong style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">2、回流焊流程介绍</strong></span><br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 回流焊加工的为表面贴装的板,其流程比较复杂,可分为两种:单面贴装、双面贴装。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> A,单面贴装:预涂锡膏 → 贴片(分为手工贴装和机器自动贴装) → 回流焊 → 检查及电测试。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> B,双面贴装:A面预涂锡膏 → 贴片(分为手工贴装和机器自动贴装) → 回流焊 →B面预涂锡膏 →贴片(分为手工贴装和机器自动贴装)→ 回流焊 → 检查及电测试。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 回流焊的最简单的流程是"丝印焊膏--贴片--回流焊,其核心是丝印的准确,对贴片是由机器的PPM来定良率,回流焊是要控制温度上升和最高温度及下降温度曲线。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <strong style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">回流焊工艺要求</strong><br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 回流焊技术在电子制造领域并不陌生,我们电脑内使用的各种板卡上的元件都是通过这种工艺焊接到线路板上的。这种工艺的优势是温度易于控制,焊接过程中还能避免氧化,制造成本也更容易控制。这种设备的内部有一个加热电路,将氮气加热到足够高的温度后吹向已经贴好元件的线路板,让元件两侧的焊料融化后与主板粘结。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 1、要设置合理的再流焊温度曲线并定期做温度曲线的实时测试。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 2、要按照PCB设计时的焊接方向进行焊接。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 3、焊接过程中严防传送带震动。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 4、必须对首块印制板的焊接效果进行检查。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 5、焊接是否充分、焊点表面是否光滑、焊点形状是否呈半月状、锡球和残留物的情况、连焊和虚焊的情况。还要检查PCB表面颜色变化等情况。并根据检查结果调整温度曲线。在整批生产过程中要定时检查焊接质量。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <span style="box-sizing: border-box !important; word-wrap: break-word !important; font-size: 16px; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px"><strong style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">影响工艺的因素:</strong></span><br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 1、通常PLCC、QFP与一个分立片状元件相比热容量要大,焊接大面积元件就比小元件更困难些。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 2、在回流焊炉中传送带在周而复使传送产品进行回流焊的同时,也成为一个散热系统,此外在加热部分的边缘与中心散热条件不同,边缘一般温度偏低,炉内除各温区温度要求不同外,同一载面的温度也差异。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 3、产品装载量不同的影响。回流焊的温度曲线的调整要考虑在空载,负载及不同负载因子情况下能得到良好的重复性。负载因子定义为: LF=L/(L+S);其中L=组装基板的长度,S=组装基板的间隔。回流焊工艺要得到重复性好的结果,负载因子愈大愈困难。通常回流焊炉的最大负载因子的范围为0.5~0.9。这要根据产品情况(元件焊接密度、不同基板)和再流炉的不同型号来决定。要得到良好的焊接效果和重复性,实践经验很重要的。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 回流焊是SMT工艺的核心技术,PCB上所有的电子元器件通过整体加热一次性焊接完成,电子厂SMT生产线的质量控制占绝对分量的工作最后都是为了获得优良的焊接质量。设定好温度曲线,就管好了炉子,这是所有PE都知道的事。很多文献与资料都提到回流焊温度曲线的设置。对于一款新产品、新炉子、新锡膏,如何快速设定回流焊温度曲线?这需要我们对温度曲线的概念和锡膏焊接原理有基本的认识。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 本文以最常用的无铅锡膏Sn96.5Ag3.0Cu0.5锡银铜合金为例,介绍理想的回流焊温度曲线设定方案和分析其原理。如图一 :</span><span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; padding-right: 0px"> <span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; padding-right: 0px"> <span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; padding-right: 0px"><span style="box-sizing: border-box !important; word-wrap: break-word !important; font-size: 14px; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px"><img alt="3.jpg" width="600" height="349" src="/d/file/jszc/2017-10-16/282c1672c3ff87917f29a9a0214f7669.jpg" /></span><span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; padding-right: 0px"><span style="box-sizing: border-box !important; word-wrap: break-word !important; font-size: 14px; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">图一 SAC305无铅锡膏回流焊温度曲线图</span><span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; padding-right: 0px"><span style="box-sizing: border-box !important; word-wrap: break-word !important; font-size: 14px; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px"><br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 图一所示为典型的SAC305合金无铅锡膏回流焊温度曲线图。图中黄、橙、绿、紫、蓝和黑6条曲线即为温度曲线。构成曲线的每一个点代表了对应PCB上测温点在过炉时相应时间测得的温度。随着时间连续的记录即时温度,把这些点连接起来,就得到了连续变化的曲线。也可以看做PCB上测试点的温度在炉子内随着时间变化的过程。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 那么,我们把这个曲线分成4个区域,就得到了PCB在通过回流焊时某一个区域所经历的时间。在这里,我们还要阐明另一个概念“斜率①”。用PCB通过回流焊某个区域的时间除以这个时间段内温度变化的绝对值,所得到的值即为“斜率”。引入斜率的概念是为了表示PCB受热后升温的速率,它是温度曲线中重要的工艺参数。图中A、B、C、D四个区段,分别为定义为A:升温区 ,B:预热恒温区(保温区或活化区),C:回流焊接区(焊接区或Reflow区),D:冷却区。</span><span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; padding-right: 0px"> <span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; padding-right: 0px"> <span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; padding-right: 0px"><img alt="4.jpg" width="600" height="345" src="/d/file/jszc/2017-10-16/34e83b6bf27ab0c978da8cdd7fb6a432.jpg" /><br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; padding-right: 0px"><span style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; color: rgb(171,25,66); padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px"><strong style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">继续深入解析个区段的设置与意义:</strong></span><span style="box-sizing: border-box !important; word-wrap: break-word !important; font-size: 14px; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px"><br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <span style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; color: rgb(123,12,0); padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px"><strong style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">一.升温区A</strong></span><br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> PCB进入回流焊链条或网带,从室温开始受热到150℃的区域叫做升温区。升温区的时间设置在60-90秒,斜率控制在2-4之间。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 此区域内PCB板上的元器件温度相对较快的线性上升,锡膏中的低沸点溶剂开始部分挥发。若斜率太大,升温速率过快,锡膏势必由于低沸点溶剂的快速挥发或者水气迅速沸腾而发生飞溅,从而在炉后发生“锡珠”缺陷。过大的斜率也会由于热应力的原因造成例如陶瓷电容微裂、PCB板变形曲翘、BGA内部损坏等机械损伤。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 升温过快的另一个不良后果就是锡膏无法承受较大的热冲击而发生坍塌,这是造成“短路”的原因之一。长期对制造厂的服务跟踪,很多厂商的SMT线该区域的斜率实际控制在1.5-2.5之间能得到满意的效果。由于各个板载贴装的元器件尺寸、质量不一,在升温区结束时,大小元器件之间的温度差异相对较大。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <span style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; color: rgb(123,12,0); padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px"><strong style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">二.预热恒温区B</strong></span><br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 此区域在很多文献和供应商资料中也称为保温区、活化区。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 该区域PCB表面温度由150℃平缓上升至200℃,时间窗口在60-120秒之间。PCB板上各个部分缓缓受到热风加热,温度随时间缓慢上升。斜率在0.3-0.8之间。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 此时锡膏中的有机溶剂继续挥发。活性物质被温度激活开始发挥作用,清除焊盘表面、零件脚和锡粉合金粉末中的氧化物。恒温区被设计成平缓升温的目的是为了兼顾PCB上贴装的大小不一的元器件能均匀升温。让不同尺寸和材料的元器件之间的温度差逐渐减小,在锡膏熔融之前达到最小的温差,为在下一个温度分区内熔融焊接做好准备。这是防止“墓碑”缺陷的重要方法。众多无铅锡膏厂商的SAC305合金锡膏配方里活性剂的活化温度大都在150-200℃之间,这也是本温度曲线在这个温度区间内预热的原因之一。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 需要注意的是:1、预热时间过短。活性剂③与氧化物反应时间不够,被焊物表面的氧化物未能有效清除。锡膏中的水气未能完全缓慢蒸发、低沸点溶剂挥发量不足,这将导致焊接时溶剂猛烈沸腾而发生飞溅产生“锡珠”。润湿不足,可能会产生浸润不足的“少锡”“虚焊”、“空焊”、“漏铜”的不良。2、预热时间过长。活性剂消耗过度,在下一个温度区域焊接区熔融时没有足够的活性剂即时清除与隔离高温产生的氧化物和助焊剂高温碳化的残留物。这种情况在炉后的也会表现出“虚焊”、“残留物发黑”、“焊点灰暗”等不良现象。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <span style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; color: rgb(123,12,0); padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px"><strong style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">三.回流焊接区C</strong></span><br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 回流区又叫焊接区或Refelow区。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> SAC305合金的熔点在217℃-218℃之间④,所以本区域为>217℃的时间,峰值温度<245℃,时间30-70秒。形成优质焊点的温度一般在焊料熔点之上15-30℃左右,所以回流区最低峰值温度应该设置在230℃以上。考虑到Sn96.5Ag3.0Cu0.5无铅锡膏的熔点已经在217℃以上,为照顾到PCB和元器件不受高温损坏,峰值温度最高应控制在250℃以下,笔者所见大部分工厂实际峰值温度最高在245℃以下。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 预热区结束后,PCB板上温度以相对较快的速率上升到锡粉合金液相线,此时焊料开始熔融,继续线性升温到峰值温度后保持一段时间后开始下降到固相线。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 此时锡膏中的各种组分全面发挥作用:松香或树脂软化并在焊料周围形成一层保护膜与氧气隔绝。表面活性剂被激活用于降低焊料和被焊面之间的表面张力,增强液态焊料的润湿力。活性剂继续与氧化物反应,不断清除高温产生的氧化物与被碳化物并提供部分流动性,直到反应完全结束。部分添加剂在高温下分解并挥发不留下残留物。高沸点溶剂随着时间不断挥发,并在回焊结束时完全挥发。稳定剂均匀分布于金属中和焊点表面保护焊点不受氧化。焊料粉末从固态转换为液态,并随着焊剂润湿扩展。少量不同的金属发生化学反应生产金属间化合物,如典型的锡银铜合金会有Ag3Sn、Cu6Sn5生成。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 回焊区是温度曲线中最核心的区段。峰值温度过低、时间过短,液态焊料没有足够的时间流动润湿,造成“冷焊”、“虚焊”、“浸润不良(漏铜)”、“焊点不光亮”和“残留物多”等缺陷;峰值温度过高或时间过长,造成“PCB板变形”、“元器件热损坏”、“残留物发黑”等等缺陷。它需要在峰值温度、PCB板和元器件能承受的温度上限与时间、形成最佳焊接效果的熔融时间之间寻求平衡,以期获得理想的焊点。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <span style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; color: rgb(123,12,0); padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px"><strong style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">四.冷却区D</strong></span><br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 焊点温度从液相线开始向下降低的区段称为冷却区。通常SAC305合金锡膏的冷却区一般认为是217℃-170℃之间的时间段(也有的文献提出最低到150℃)。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 由于液态焊料降温到液相线以下后就形成固态焊点,形成焊点后的质量短期内肉眼无法判断,所以很多工厂往往不是很重视冷却区的设定。然而焊点的冷却速率关乎焊点的长期可靠性,不能不认真对待。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 冷却区的管控要点主要是冷却速率。经过很多焊锡实验室研究得出的结论:快速降温有利于得到稳定可靠的焊点。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 通常人们的直觉认为应该缓慢降温,以抵消各元器件和焊点的热冲击。然而,回流焊锡膏钎焊慢速冷却会形成更多粗大的晶粒,在焊点界面层和内部生较大Ag3Sn、Cu6Sn5等金属间化合物颗粒。降低焊点机械强度和热循环寿命,并且有可能造成焊点灰暗光泽度低甚至无光泽。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 快速的冷却能形成平滑均匀而薄的金属间化物,形成细小富锡枝状晶和锡基体中弥散的细小晶粒,使焊点力学性能和可靠性得到明显的提升与改善。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 生产应用中,并不是冷却速率越大越好。要结合回流焊设备的冷却能力、板子、元器件和焊点能承受的热冲击来考量。应该在保证焊点质量时不损害板子和元器件之间寻求平衡。最小冷却速率应该在2.5℃以上,最佳冷却速率在3℃以上。考虑到元器件和PCB能承受的热冲击,最大冷却速率应该控制在6-10℃。工厂在选择设备时,最好选择带水冷功能的回流焊而获得较强的冷却能力储备。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <span style="box-sizing: border-box !important; word-wrap: break-word !important; font-size: 16px; max-width: 100%; color: rgb(123,12,0); padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px"><strong style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">3、回流焊技术有那些优势?</strong></span><br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 1)再流焊技术进行焊接时,不需要将印刷电路板浸入熔融的焊料中,而是采用局部加热的方式完成焊接任务的;因而被焊接的元器件受到热冲击小,不会因过热造成元器件的损坏。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 2)由于在焊接技术仅需要在焊接部位施放焊料,并局部加热完成焊接,因而避免了桥接等焊接缺陷。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 3)再流焊技术中,焊料只是一次性使用,不存在再次利用的情况,因而焊料很纯净,没有杂质,保证了焊点的质量。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <span style="box-sizing: border-box !important; word-wrap: break-word !important; font-size: 16px; max-width: 100%; color: rgb(123,12,0); padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px"><strong style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">4、回流焊的注意事项</strong></span><br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 1.桥联<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 回流焊焊接加热过程中也会产生焊料塌边,这个情况出现在预热和主加热两种场合,当预热温度在几十至一百度范围内,作为焊料中成分之一的溶剂即会降低粘度而流出,如果其流出的趋势是十分强烈的,会同时将焊料颗粒挤出焊区外的含金颗粒,在熔融时如不能返回到焊区内,也会形成滞留的焊料球。 除上面的因素外,SMD元件端电极是否平整良好,电路线路板布线设计与焊区间距是否规范,阻焊剂涂敷方法的选择和其涂敷精度等都会是造成桥联的原因。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 2.立碑元件浮高(曼哈顿现象)<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 片式元件在遭受回流焊急速加热情况下发生的翘立,这是因为急热使元件两端存在温差,电极端一边的焊料完全熔融后获得良好的湿润,而另一边的焊料未完全熔融而引起湿润不良,这样促进了元件的翘立。因此,回流焊加热时要从时间要素的角度考虑,使水平方向的加热形成均衡的温度分布,避免回流焊急热的产生。 <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 防止元件翘立的主要因素有以下几点: <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> ①选择粘接力强的焊料,焊料的印刷精度和元件的贴装精度也需提高; <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> ②元件的外部电极需要有良好的湿润性和湿润稳定性。推荐:温度40℃以下,湿度70%RH以下,进厂元件的使用期不可超过6个月; <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> ③采用小的焊区宽度尺寸,以减少焊料熔融时对元件端部产生的表面张力。另外可适当减小焊料的印刷厚度,如选用100μm; <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> ④焊接温度管理条件设定也是元件翘立的一个因素。通常的目标是加热要均匀,特别在元件两连接端的焊接圆角形成之前,均衡加热不可出现波动。<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 3.润湿不良<br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 润湿不良是指回流焊焊接过程中焊料和电路基板的焊区(铜箔)或SMD的外部电极,经浸润后不生成相互间的反应层,而造成漏焊或少焊故障。其中原因大多是焊区表面受到污染或沾上阻焊剂,或是被接合物表面生成金属化合物层而引起的。譬如银的表面有硫化物、锡的表面有氧化物都会产生润湿不良。另外焊料中残留的铝、锌、镉等超过0.005%以上时,由于焊剂的吸湿作用使活化程度降低,也可发生润湿不良。因此在焊接基板表面和元件表面要做好防污措施。选择合适的焊料,并设定回流焊合理的焊接温度曲线。 <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <span style="box-sizing: border-box !important; word-wrap: break-word !important; font-size: 16px; max-width: 100%; color: rgb(123,12,0); padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px"><strong style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">无铅焊接的五个步骤:</strong> </span><br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 1、选择适当的材料和方法 <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 在无铅焊接工艺中,焊接材料的选择是最具挑战性的。因为对于无铅焊接工艺来说,无铅焊料、焊膏、助焊剂等材料的选择是最关键的,也是最困难的。在选择这些材料时还要考虑到焊接元件的类型、线路板的类型,以及它们的表面涂敷状况。选择的这些材料应该是在自己的研究中证明了的,或是权威机构或文献推荐的,或是已有使用的经验。把这些材料列成表以备在工艺试验中进行试验,以对它们进行深入的研究,了解其对工艺的各方面的影响。 <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 对于焊接方法,要根据自己的实际情况进行选择,如元件类型:表面安装元件、通孔插装元件;线路板的情况;板上元件的多少及分布情况等。对于表面安装元件的焊接,需采用回流焊的方法;对于通孔回流焊插装元件,可根据情况选择波峰焊、浸焊或喷焊法来进行焊接。波峰焊更适合于整块板(大型)上通孔插装元件的焊接;浸焊更适合于整块板(小型)上或板上局部区域通孔插装元件的回流焊焊接;局喷焊剂更适合于板上个别元件或少量通孔插装元件的回流焊焊接。另外,还要注意的是,无铅回流焊焊接的整个过程比含铅焊料的要长,而且所需的焊接温度要高,这是由于无铅焊料的熔点比含铅焊料的高,而它的浸润性又要差一些的缘故。 在焊接方法选择好后,其焊接工艺的类型就确定了。这时就要根据焊接工艺要求选择设备及相关的工艺控制和工艺检查仪器,或进行升级。焊接设备及相关仪器的选择跟焊接材料的选择一样,也是相当关键的。 <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 2、确定工艺路线和工艺条件 <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 在第一步完成后,就可以对所选的焊接材料进行焊接工艺试验。通过试验确定工艺路线和工艺条件。在试验中,需要对列表选出的焊接材料进行充分的试验,以了解其特性及对工艺的影响。这一步的目的是开发出无铅焊接的样品。 <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 3、开发健全焊接工艺 <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 这一步是第二步的继续。它是对第二步在工艺试验中收集到的试验数据进行分析,进而改进材料、设备或改变工艺,以便获得在实验室条件下的健全工艺。在这一步还要弄清无铅合金焊接工艺可能产生的沾染知道如何预防、测定各种焊接特性的工序能力(CPK)值,以及与原有的锡/铅工艺进行比较。通过这些研究,就可开发出焊接工艺的检查和测试程序,同时也可找出一些工艺失控的处理方法。 <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 4、还需要对焊接样品进行可靠性试验,以鉴定产品的质量是否达到要求。如果达不到要求,需找出原因并进行解决,直到达到要求为止。一旦焊接产品的可靠性达到要求,无铅焊接工艺的开发就获得成功,这个工艺就为规模生产做好了准准备就绪后的操作一切准备就绪,现在就可以从样品生产转变到工业化生产。在这时,仍需要对工艺进行以维持工艺处于受控状态。 <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 5、控制和改进工艺 <br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> 无铅焊接工艺是一个动态变化的舞台。工厂必须警惕可能出现的各种问题以避免出现工艺失控,同时也还需要不断地改进工艺,以使产品的质量和合格晶率不断得到提高。对于任何无铅焊接工艺来说,改进焊接材料,以及更新设备都可改进产品的焊接性能。</span><span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p> <span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; white-space: normal; word-spacing: 0px; text-transform: none; color: rgb(62,62,62); padding-bottom: 0px; padding-top: 0px; font: 16px/25px 'Helvetica Neue', Helvetica, 'Hiragino Sans GB', 'Microsoft YaHei', Arial, sans-serif; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; widows: 1; letter-spacing: normal; padding-right: 0px; background-color: rgb(255,255,255); text-indent: 0px; -webkit-text-stroke-width: 0px"><br style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px" /> <span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <hr style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; white-space: normal; word-spacing: 0px; text-transform: none; color: rgb(62,62,62); padding-bottom: 0px; padding-top: 0px; font: 16px/25px 'Helvetica Neue', Helvetica, 'Hiragino Sans GB', 'Microsoft YaHei', Arial, sans-serif; padding-left: 0px; margin: 0px; widows: 1; letter-spacing: normal; padding-right: 0px; background-color: rgb(255,255,255); text-indent: 0px; -webkit-text-stroke-width: 0px" /> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; white-space: normal; word-spacing: 0px; text-transform: none; color: rgb(62,62,62); padding-bottom: 0px; text-align: left; padding-top: 0px; font: 16px/25px 'Helvetica Neue', Helvetica, 'Hiragino Sans GB', 'Microsoft YaHei', Arial, sans-serif; padding-left: 0px; clear: both; margin: 0px; min-height: 1em; widows: 1; letter-spacing: normal; padding-right: 0px; background-color: rgb(255,255,255); text-indent: 0px; -webkit-text-stroke-width: 0px"><span style="color: #ff0000"><span style="font-size: small"><strong><span style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">往</span></strong></span></span><section style="box-sizing: border-box !important; word-wrap: break-word !important; font-size: 20px; max-width: 100%; height: 40px; width: 40px; background: rgb(229,51,16); color: rgb(255,255,255); padding-bottom: 0px; text-align: center; padding-top: 0px; padding-left: 0px; margin: 0px 10px 0px 0px; line-height: 40px; padding-right: 0px"></section><span style="color: #ff0000"><span style="font-size: small"><strong><span style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">期</span></strong></span></span><section style="box-sizing: border-box !important; word-wrap: break-word !important; font-size: 20px; max-width: 100%; height: 40px; width: 40px; background: rgb(229,51,16); color: rgb(255,255,255); padding-bottom: 0px; text-align: center; padding-top: 0px; padding-left: 0px; margin: 0px 10px 0px 0px; line-height: 40px; padding-right: 0px"></section><span style="color: #ff0000"><span style="font-size: small"><strong><span style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">文</span></strong></span></span><section style="box-sizing: border-box !important; word-wrap: break-word !important; font-size: 20px; max-width: 100%; height: 40px; width: 40px; background: rgb(229,51,16); color: rgb(255,255,255); padding-bottom: 0px; text-align: center; padding-top: 0px; padding-left: 0px; margin: 0px; line-height: 40px; padding-right: 0px"></section><span style="color: #ff0000"><span style="font-size: small"><strong><span style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; padding-right: 0px">章</span></strong></span></span><span style="display:none">vyESMT技术网-China表面贴装技术-SMT表面贴装-SMT技术网【官网】</span></p> <p style="box-sizing: border-box !important; word-wrap: break-word !important; max-width: 100%; white-space: normal; word-spacing: 0px; text-transform: none; 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