| 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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What are the key steps to achieving high yield with CSP ??...
- Aug 26, 1999
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