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PCB007-Sep2021

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66 PCB007 MAGAZINE I SEPTEMBER 2021 Introduction Over the past 18 years or so, my columns have focused on presenting a specific defect or defects, drilling down to the root causation of the defect, and quickly and efficiently identi- fying and subsequently eliminating the cause. For this month's edition, we are taking a slight- ly different approach—that of presenting an actual case study. However, the basic princi- ples of these columns continue. The Issue e situation involves a large and well- equipped printed circuit board fabricator. e company had received returns for what was viewed as Type 1 ICDs; the electroless copper was pulling away from the interconnect. As is so oen the case with defects, the non-con- Case Study—Interconnect Defects and a Few Other Problems formance was only detected on a few panels. ere was no correlation to the part design. All panels exhibiting the problem were multilay- ers, either 10 or 12 layers, with standard FR-4 construction. Microsectional analysis showed the problem (Figure 1). e desmear/etchback was deemed suf- ficient. With such a degree of etchback, no smear should have remained. So, what was the cause of this issue? Again, the defect was only seen on a few isolated oc- casions. Further examination of sections aer plating showed some interesting anomalies. Figure 2 shows a closer view of the inter- connect. Looking closely at the section, one can see debris on the face of the interconnect. Clearly, the debris is the major reason why the electroless is not making contact with the Trouble in Your Tank by Michael Carano, RBP CHEMICAL TECHNOLOGY Figure 1: After 550°F solder float for 10 seconds. Separation noted on sections prior to etching the specimen. Figure 2: Clearly there is insoluble material interfering with the adhesion of the electroless deposit.

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