| Hi all , | | We are trying to implement the micro-BGA technology at our plant. I need the clarification to the following points: | | 1. Is underfill required for micro-BGAs? | | 2. What type of stencil apertures are the industry standards for uBGAs and of what size and thickness.? | | Thanks and regards | Upinder | ====== | Upinder,
Underfill is not needed, depending on the application (aerospace with harsh environments as continuous thermal and mechanical shock) and part density. We are doing .5mm without it. Our .8mm devices use .017" pads with a stencil aperture about .020" round in 6 mil thick stencil foils.
I am still working on optimizing .5mm uBGA requirements though 4-5 mil stencil thicknesses (stepped down as needed from 6 mils) with nearly 1:1 aperture to pad ratios look good as little shorting at X-Ray is apparent using nearly standard reflow profiles as for most BGA types.
We experience little rework. When needed, we use micro stencils to print paste for .8mm types. With those below, we use a syringe method to apply paste (see Blankenhorn's stuff).
I'm a late starter in .5mm types. Where is Justin when you need him? I think he was doing this stuff over a year ago and probably has lots of reliabillity data I've not yet developed.
I'm looking for 500 to 1,500 T/M cycles to failure using dummies with TDR testing not exceeding 300 ohms - hopefully less. Also looking at X-Sections with certain failures.
Earl Moon
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