Thursday, 11 February 2016

BGA on a budget

After months of trying to find a reasonably priced PCB manufacturer that offered a spec good enough for 0.8mm pitch BGA parts, I gave up and cheated! As soon as you want below 6mil (or 5 for oshpark I think), or below 12mil vias, the price goes in to the $100+ range for a small board. I wasn't going to spend that amount so I thought I'd push my luck a bit and go under spec and see what I got back. Their website specs I was presuming allowed for a better yield so costs stay down for them. I was honest and left a comment saying I was under spec and would accept any/all failed boards... so there was no risk or loss for them even if the whole batch was unusable. Obviously I didn't reduce drill sizes or anything.

Left: Official DRC in place, 6/6/12 (>=6 annular rings)
Right: Adjusted rules, 6/4/12 (4mil annular rings)

For the real boards I only reduced the specs where necessary, under the BGA part. The rest of the board met the requirements. Here's what I ended up with (success!)

All of the 10 were OK for the BGA part (some better than others), but weirdly 3 were unusable in other (in-spec) areas because of drill alignment problems. Even though I only went for HASL finish and had never previously soldered a BGA part, it went straight on and works fine. Not really sure what all the fuss is about! People complain about the fact you need an xray to check for faults... but these things have boundary scan... I mean that's what JTAG was invented for, right?

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