Hi,



Firstly, I would like to explain that the Omegameter is mainly designed for

testing of the board / assembled board after clean (either by water or

organic solvent).  Certainly, some customers may use it as the process

control in their no-clean process but the pass/fail limit should be

reviewed.



If using the no-clean material especially with solder paste,  the solvency

of extracted solution (IPA + DI water) from Omegameter is not sufficient to

totally dissolve the residue from the board.  Therefore, you would observe

the white residue after test............ that means........ only partial

dissolution.  When you test two no-clean pastes even under the same

condition and then find out the difference in readings, it does not means

that Paste A has higher ionic contaminaiton than Paste B........... the

result may only reflect the difference in the solubility of the residue

from the paste into the extracted solution in Omegameter.  Better

solubility of residue to solvent, higher reading obtained ......... but

does not refect the real total ionic contamination from each paste.



For the area calculation, it should be the wetted area of the component +

board.  It is quite difficult to calculate accurately.  Therefore, the

standard suggests the estimation method such as you mentioned below.



The amount of residue left after wavesoldering depends on:



1. Flux



2. Amount of flux applied



3. Contact time



4. Single wave or dual wave



5. The solder mask characteristics



As for the solder pad 's quantity and distribution, it would affect the

distribution of flux residue.



As for the cleanliness level of PCB,  bellcore spec is said  < 1 ug/ sq. cm

while IPC 6012 is said < 1.56 ug/cmin or based on procurement document.  In

the industry, tighen level is normally encountered for PCB board  For

example, some request < 0.5 ug/sq. cm



Jackson Chan

Technical Services Manager



Cookson Electronics - Alpha Metals

(Low cost, high reliability alloy - SACX0807)





                                                                           

             谢宏涛                                                        

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             2008/06/13 下午                                       Subject 

             02:15                     [TGA] 离子洁净度测试问题多多，恳请  

                                       各位指教                            

                                                                           

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大家好：

    我们现在正在做一个国产化项目，外方没有PCBA的生产能力，以前都是由国际知

名生产厂家代工的。现在外方人员给我们只能提供一些他们在代工方得到的工艺路

线，并要求我们按照他们的工艺路线和指定的焊膏、助焊剂生产。

        外方提供信息：

         焊膏：alpha UP-78，为免清洗型

         波峰助焊剂：alphar330，为免清洗助焊剂

        工艺路线：丝网印->回流焊->波峰焊->水清洗->手工补焊->手工清洗

->ICT->涂敷

        要求波峰焊接完成后，要进行水清洗，并且最终产品离子洁净度小于1.56μg

NaClEq./cm2

    在试生产中发现离子洁净度比原来我们厂生产的板子高，并且有点靠近

IPC-TM-650中的最大值1.56μg NaCl Eq./cm2，所以使用OMEGA METER 600-SMD做了一

些试验性测试。测试情况如下：

         1、在两块相同裸板上使用两种焊膏印刷->过回流->水清洗->洁净度测试

（试验3次）

                 焊膏1：alpha UP-78          0.7、0.3、0.5 μg

NaClEq./cm2（2倍板面积）

                 焊膏2：asahi Sn633-5T-E  0.2 、0.0、0.2μg NaClEq./cm2（2倍

板面积）

         2、测试PCB裸板，得出裸板清洁度为0.3 μg NaClEq./cm2（2倍板面积）

         现在我的问题是：

                1、洁净度测试时的PCBA板面积计算不好把握。IPC650只提供了一个

大概值：(Length x Width x 2) + up to 50%，这在测试时很难把握，对结果影响很

大；

                2、洁净度测试完成后，焊点周围出现了白色粉末状固体，不知是什

么原因造成的；

                3、这种焊膏、波峰助焊剂跟我们的工序是否有不合理的地方；

                4、波峰助焊剂的残留是否与PCB上的辅面焊盘数量和密度有关；

                5、PCB生产厂家出厂的离子洁净度应该在什么范围内；



    因为经验不足，这些问题一直不能解决。恳请各位多提意见，谢谢！！！



                                                            谢宏涛











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