Why to do mixed surface treatment?

First of all, let’s take a look at this example of case,the context is that there was a project with BGA balls, but the BGA balls were peeled off in the thermal shock. We reviewed all production records and inspection results and excluded the possibility of everything except the reason of gold thickness.The good thickness for this project is 3u”(0.0762um).

You must be curious about this conclusion, why the gold thickness?From the standpoint of a manufacturer,we often find some customer defined mixed surface finish (ENIG + OSP), ENIG for the exposed copper pads(but BGA area), OSP for BGA balls. Why are the customer defining mixed surface finish? The reason is to avoid BGA balls peel off from the base material.

Why to do Mixed surface treatment?

—— The relation with gold thickness and SMT

First of all, let’s take a look at this example of case,the context is that there was a project with BGA balls,but the BGA balls were peeled off in the thermal shock.We reviewed all production records and inspection results and excluded the possibility of everything except the reason of gold thickness.The good thickness for this project is 3u”(0.0762um).

I think you must be curious about this conclusion,why the gold thickness?

From the standpoint of a manufacturer,we often find some customer defined mixed surface finish (ENIG + OSP),ENIG for the exposed copper pads(but BGA area),OSP for BGA balls. Why are the customer defining mixed surface finish? The reason is to avoid BGA balls peel off from the base material.

The thicker gold thickness the more time spend of gold melted when we do PCB assembly.We can reduce the gold thickness to 1-2u” or change the surface finish to ENIG+OSP.

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