TC 1.3

Why Clean a No-Clean Flux

Mike Bixenman

Residues present on circuit boards can cause leakage currents if not controlled and monitored. How “Clean is Clean” is neither easy nor cheap to determine. Most OEMs use analytical methods to assess the risk of harmful residues. The levels that can be associated with clean or dirty are typically determine based on the exposed environment where the part will be deployed. What is acceptably clean for one segment of the industry may be unacceptable for more demanding segments. 

As circuit assemblies increase in density, understanding cleanliness data becomes more challenging. The risk of premature failure or improper function is typically site specific. The problem is that most do not know how to measure or define cleanliness nor can they recognize process problems related to residues. A new site specific method has been designed to run performance qualifications on boards built with specific soldering materials, reflow settings and cleaning methods. High impedance measurements are performed on break off coupons designed with components geometries used to build the assembly. The test method provides a gauge of potential contamination sources coming from the assembly process that can contribute to electrochemical migration.

 

为何需要清洗免洗助焊剂

电路板上的助焊剂残留如果没有适当控制和监控可能会引起漏电。多干净才算是干净?这个问题不好定义,也不能轻易定义。大部分原始设备制造商采用分析法来评估有害残留的风险。与干净或肮脏有关的风险水平通常根据相关部件使用时所暴露的环境来确定。某干净的程度在一个行业某部份设备能被接受但在另一个要求更高的部份可能就无法满足要求。

由于电路板组件密度不断增高,对于清洁度数据的理解将变得更加困难。过早失效或功能异常等风险通常只发生在特定区域。但是问题在于,大部分人不懂的如何测量或定义清洁度,他们也无法识别与残留有关的工艺问题。我们已经设计出一种全新的定点方法,针对采用特定焊料、回流设定和清洗方法的电路板进行性能合格测试。针对断开后的几何元件试片,我们进行了高阻抗测量。测试方法为来自组件工艺流程且可能产生电化学迁移的潜在污染源提供了测量工具。

 

 

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