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Processing questions - PCB and BGA's

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Processing questions - PCB and BGA's | 30 January, 2009

We have a potential new customer who has special PCB requirements. I do not know a lot of details at this point, but have several questions.

One of their assemblies has within it , a MID, Solid foil layer, completely isolating one side of the PCB from the other. Basically like having two boards with a solid shield (no vias within).

While I do not currently know the material, does anyone out there have experience with this type PCB? Are you familiar with this type board and are you aware of any special processing requirements (primarily thermal) to prevent warping, delamination,etc.?

This same customer has another assembly that has a multi layer board, however the sides are plated, much like gold fingers, but this plating is 100% around the perimeter edges. The purpose of this is to basically seal the laminate from moisture. The same questions above apply, especially any special handling to prevent plating damage.

A third question, concerning sealing BGA's. This customer has had field failures as a result of moisture ingress under the part (I do not currrently know the environment), despite the assembly being conformal coated. Whatever solution is determined to be effective must be re-workable, which leaves RTV or potting material and such materials (customer mentioned this not us) out of the question. What is available (product or process) to seal the perimeter of BGA packages totally?

As always, appreciate any insights you might provide.

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Processing questions - PCB and BGA's | 30 January, 2009

I do a lot of thermal cycle testing of new components for my company and often when I lay out a test board I'm trying to simulate 4 or 6 layer boards but I don't need them for routing so I just use a solid fill of a cross-hatch pattern. I've done it lots of times with 0.031", 0.047", and 0.062" thick boards and have never had a problem with warping. My test boards tend to be 6"x8" or 4"x6" so they aren't huge.

Sorry, I can't offer anything on your other two questions. We've never plated the board edge. We do a lot of conformal coating and also a lot of capillary underfill of flipchips, but have never tried to do some type of perimeter dispense to keep moisture out.

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