The Difficulty of Tiny PCBs at Home
October 18, 2020
At-home PCB work becomes a different problem at tiny pitch. The obstacle is not only drawing a trace once; it is making the same trace, hole, pad, and layer alignment repeatably.
This note names the process boundary found at the time: around 0.5 mm for repeatable multilayer prototyping, with smaller features failing through non-conducting holes, bridged pads, glue spread, etch spread, or alignment error.
PCB process noteOriginally posted 2020-10-18; expanded here around the repeatability limit.
Article focus: 6 mil traces, 0.35 mm BGAs, at-home multilayer process limits, and repeatable feature size.
The Boundary
The target cases were small: 6 mil PCB features and 0.35 mm BGA soldering. At that scale, low-cost commercial PCB services begin to look inexpensive because they are selling repeatability, not just copper and substrate.
The at-home process experiments included laser cutter, laser printer, photoresist, ferric chloride, silver paste, vinyl layers, copper film, and Avery sticker masks. The observed practical boundary was around 0.5 mm for repeatable multilayer prototyping.
Failure Modes
Two failures dominated the note: holes that stopped conducting and neighboring pads that bridged. At small geometry, glue and etchant movement become electrical problems. Alignment and process control matter as much as the nominal feature size.
That is the engineering value of the note: home fabrication has to be judged by repeatable yield, not by whether one small feature can be made once.