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Achieving High Yields with CSP

Stuart Adams

#9922

Achieving High Yields with CSP | 26 August, 1999

What are the key steps to achieving high yield with CSP ???

(We are trying qualify vendors for volume fab/assembly of some products which use several CSP devices on each side of the board. (Some with 0.5mm ball pitch))

Looking through the forum I found some of the following suggestions. What else am I missing ???

PCB Fab: Don't use Tin/HASL. Gold seems to be the #1 choice.

Solder-Stencil: Use square tapered aperatures ??

Solder-Paste: Any special application prodecure ?? Is in-line inspection of paste required ??

Placement: 0.1mm or better placement accuracy. Anything else ??

Reflow and Cleaning ???

Thanks, Stuart sja@world.std.com

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Earl Moon

#9923

Re: Achieving High Yields with CSP | 26 August, 1999

| What are the key steps to achieving high yield with CSP ??? | | (We are trying qualify vendors for volume fab/assembly of some | products which use several CSP devices on each side of the | board. (Some with 0.5mm ball pitch)) | | Looking through the forum I found some of the following | suggestions. What else am I missing ??? | | PCB Fab: | Don't use Tin/HASL. Gold seems to be the #1 choice.

Watch the solder mask as well and we had good success with OSP/OCC coatings. | | Solder-Stencil: | Use square tapered aperatures ??

Still haven't used square anyting with BGA's including micro stencils for rework - something else to consider with at least .200" all around the nozzle, or? | | Solder-Paste: | Any special application prodecure ?? | Is in-line inspection of paste required ??

Keep the stencil apertures clean. In line inspection is a luxury we didn't have in my last contract - here we have it but just wringing it out for BGA and fine pitch. Still rely heavily on X-Ray for protos to find shorts and correct problems. Used constant tension Tetra foils last time out and prevented lots of problems. | Placement: | 0.1mm or better placement accuracy. | Anything else ??

Haven't done .5's but have done many .8's. Can't do DFM for repair yet with .5's. .8's stretching the envelope - leading to 25% maximum mis-prints and alignment - after that they suck into self alignment very well so placement accuracy considered on that basis but most placement and printing equipment capable.

| Reflow and Cleaning ???

Again, we use now, as former contract, the same paste and very basic profiles using no clean and nitrogen. No big deal yet. | | Thanks, | Stuart | sja@world.std.com

Earl Moon |

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swsng

#9924

Re: Achieving High Yields with CSP | 27 August, 1999

| What are the key steps to achieving high yield with CSP ??? | | (We are trying qualify vendors for volume fab/assembly of some | products which use several CSP devices on each side of the | board. (Some with 0.5mm ball pitch)) | | Looking through the forum I found some of the following | suggestions. What else am I missing ??? | | PCB Fab: | Don't use Tin/HASL. Gold seems to be the #1 choice. | | Solder-Stencil: | Use square tapered aperatures ?? | | Solder-Paste: | Any special application prodecure ?? | Is in-line inspection of paste required ?? | | Placement: | 0.1mm or better placement accuracy. | Anything else ?? | | Reflow and Cleaning ??? | | Thanks, | Stuart | sja@world.std.com | | Average stencil opening for 12mils csp =15mils opening and 20mils Mbga ave.=17mils opening sq opening while placement use a special square nozzle with zero placement force <50 gmf 2d all balls check

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