Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Parvez Patel

#12830

Assembly of CSP on pads with vias. | 23 January, 1999

Hi Everyone, We plan to build, for reliability/experimental/research purpose some CSPs (namely Tessera microBGA 46-I/O 0/75mm pitch and TI 64 I/O 0/8 mm pitch). the various factors that we plan to evaluate are the reliability and assembly concerns for four diff pad types: full microvia in pad, partial via in pad, the dog bone and the normal circular pad design. We also plan to play around with the permissible placement offsets that these pads can take with allowable self centering. I would really appreciate if anyone of u cud tell me the DOs and DONTs before we embark on the experimental design. Also any type of trends that u all have found for for similar experiments. Thanks in anticipation Regards

Parvez Patel Graduate Research Associate Universal Instruments Corporation Binghamton-NY 13905 Ph: 607-779-7215

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Earl Moon

#12831

Re: Assembly of CSP on pads with vias. | 23 January, 1999

| Hi Everyone, | We plan to build, for reliability/experimental/research purpose some CSPs (namely Tessera microBGA 46-I/O 0/75mm pitch and TI 64 I/O 0/8 mm pitch). the various factors that we plan to evaluate are the reliability and assembly concerns for four diff pad types: full microvia in pad, partial via in pad, the dog bone and the normal circular pad design. | We also plan to play around with the permissible placement offsets that these pads can take with allowable self centering. | I would really appreciate if anyone of u cud tell me the DOs and DONTs before we embark on the experimental design. Also any type of trends that u all have found for for similar experiments. | Thanks in anticipation | Regards | | | Parvez Patel | Graduate Research Associate | Universal Instruments Corporation | Binghamton-NY 13905 | Ph: 607-779-7215 | | Parvez,

I've been down, and continue, this path many times. In 1982, I created standard hole in pad configurations using sequential lamination and plating over the remaining hole in pad structure so no hole was apparent. This was a very reliable situation because it relied on proven technology.

In 1993, I used standard, high aspect ratio, plated through holes (10:1 as 6 mil holes in .062" thick MLB's) in BGA pads and as blind vias in same. Of course, the through holes didn't work well because of solder drain off. The blind vias worked well but some outgassing was apparent - depending on flux, paste, and profiles.

The problems I'm finding with micro-vias is similar as far as some outgassing - depending on depth through the outers. The biggest problems concern fabrication relative to hole wall preparation (etch back, etc.), electroless copper deposition (very often inconsistet), and electroplated copper often low on ductillity and also inconsistent.

I have much more, but no time here to say it.

Have a grand experiment,

Earl Moon

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Steve Gregory

#12832

Re: Assembly of CSP on pads with vias. | 23 January, 1999

| Hi Everyone, | We plan to build, for reliability/experimental/research purpose some CSPs (namely Tessera microBGA 46-I/O 0/75mm pitch and TI 64 I/O 0/8 mm pitch). the various factors that we plan to evaluate are the reliability and assembly concerns for four diff pad types: full microvia in pad, partial via in pad, the dog bone and the normal circular pad design. | We also plan to play around with the permissible placement offsets that these pads can take with allowable self centering. | I would really appreciate if anyone of u cud tell me the DOs and DONTs before we embark on the experimental design. Also any type of trends that u all have found for for similar experiments. | Thanks in anticipation | Regards | | | Parvez Patel | Graduate Research Associate | Universal Instruments Corporation | Binghamton-NY 13905 | Ph: 607-779-7215

Hello there Parvez!

I've placed a lot of 46-ball Tessera microBGA's. We used to build these little "keychain fobs" that we passed out at trade shows like NEPCON and the like.

There's one thing about your stencil for microBGA that I learned that really helps a lot. Make your apertures square instead of round in the stencil. Paste releases from the stencil better, gives ya' a little more slop for placement, and a little more volume for the joints...it'll all wick together during reflow, so don't be worried about solder balls.

-Steve Gregory-

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Earl Moon

#12833

Re: Assembly of CSP on pads with vias. | 23 January, 1999

| | Hi Everyone, | | We plan to build, for reliability/experimental/research purpose some CSPs (namely Tessera microBGA 46-I/O 0/75mm pitch and TI 64 I/O 0/8 mm pitch). the various factors that we plan to evaluate are the reliability and assembly concerns for four diff pad types: full microvia in pad, partial via in pad, the dog bone and the normal circular pad design. | | We also plan to play around with the permissible placement offsets that these pads can take with allowable self centering. | | I would really appreciate if anyone of u cud tell me the DOs and DONTs before we embark on the experimental design. Also any type of trends that u all have found for for similar experiments. | | Thanks in anticipation | | Regards | | | | | | Parvez Patel | | Graduate Research Associate | | Universal Instruments Corporation | | Binghamton-NY 13905 | | Ph: 607-779-7215 | | Hello there Parvez! | | I've placed a lot of 46-ball Tessera microBGA's. We used to build these little "keychain fobs" that we passed out at trade shows like NEPCON and the like. | | There's one thing about your stencil for microBGA that I learned that really helps a lot. Make your apertures square instead of round in the stencil. Paste releases from the stencil better, gives ya' a little more slop for placement, and a little more volume for the joints...it'll all wick together during reflow, so don't be worried about solder balls. | | -Steve Gregory- | | | Steve,

Nice work again. What you suggested really works well - like you needed to hear that from me. No matter, are you going to be an IPC "legend" for sure? I still don't know because of my work schedule up here in the frozen "Tundra."

MoonMan

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