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ENIG again! Failed BGA joint!

sinclair

#6506

ENIG again! Failed BGA joint! | 8 May, 2001

We started our first ENIG process recently and to our surprise, we have many failure on the one and only BGA on the board. The BGA is a 31 mils pitch plastic. Sending the PCBA to 1 cycle of heating/cooling @ 70/-5 degree C yield 40% of failure. With such high reject, those that pass testing could be faulty and those that fail test may pass again. We ply the joint apart. Physically about 90+% of joint break-off at the pad. About 30% of the pad is flat (sign of no wetting) or partially soldered. One failed part was send for XPS and 2 joints were analyzed. One of the joint has 2 elements that we think is abnormal: Zn and Si. Also there is no sign of Pb!!! We suspect Si could come from the BGA packaging. Anyone can help to shed some light and explain what we are seeing? Possible solution/recommendation is appreciated. Thanks you. (Note the same BGA package is used on other product on a HAL PCB w/o any failure. So we think part of the problem is in the ENIG PCB. The plating thickness is spec at 4 micron)

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#6515

ENIG again! Failed BGA joint! | 8 May, 2001

It�s reasonable to want to understand this strange looking fabrication, before moving on to other issues.

Before moving on to that, tell us more about your thinking the silicon being from the BGA package. What kind of plastic package is this?

Describe [eg, texture, color, etc] the surface that failed to solder.

What level of potassium did your analysis show?

You are almost certainly not picking up pure silicon, the element. You could be picking up a compound of silicon, which could even be glass. Thing to consider are: * Does your fab use presses to laminate rigid boards, which have glass fiber reinforcing them?? * Could it might be residue from a pumice scrub that�s embedded into the pads. * Could it be a silicon based anti-foam that was not rinsed from the pads properly. * Some desiccants give off a silicon oxide vapor. Is this inhibiting your soldering operations? * May be the compounds are organic silicon compounds, silicones. [As a sailors, we used to go see Carol Doda, now high school girl use the stuff.]

How do you think your problem relates to the "black pad" problem in ENIG?

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CAL

#6516

ENIG again! Failed BGA joint! | 8 May, 2001

www.empf.org empfasis news letter March 2001 issue "Manufacturing with BGA's"

Reading this while impersonating Elvis will generate best results.

Caldon W. Driscoll ACI USA 610-362-1200 cdriscoll@aciusa.org

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Michael Parker

#6518

ENIG again! Failed BGA joint! | 8 May, 2001

Carol Doda?!!! She retired from the Condor club about 15 years ago. As for reference to all the other Plastics Princesses - God bless 'em all!!! 'Tis the time of year for halter tops and shorts - ye haw!

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#6528

ENIG again! Failed BGA joint! | 9 May, 2001

Retired!!!! Well, that certainly explains why I keep getting my Christamas cards returned, unopened!!!!

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