Andrew Zonenberg on Nostr: So BGAs have been a bit of a pain in my behind for a while from an IC RE perspective. ...

So BGAs have been a bit of a pain in my behind for a while from an IC RE perspective.

Specifically, wirebonded BGAs with multilayer organic substrates. I use 70% nitric acid at home for decapsulation rather than fuming (more stable in storage, safer to work with, and far easier/less expensive to source) which doesn't do a great job of etching the BT resin compared to the silica filled molding compound.

Usually what happens is that the overmold disintegrates rapidly leaving the bare die stuck to a slab of fiberglass, then the substrate slooooowly decomposes over the course of 30+ minutes with the die slowly being damaged by bond pad underetch, banging into debris in the beaker, repeated cleaning and handling steps, etc.

So as an experiment, I'm trying a different strategy: use 220 grit wet sanding, by hand, to remove the substrate before switching to chemical processing.

As a bonus, if you work carefully and take photos at intermediate steps it should be possible to reconstruct most/all of the substrate netlist and figure out the mapping of BGA lands to wire bond pads.

Here's a very old Artix-7 part (from before they started putting datamatrix codes on them)