Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It only takes a minute to sign up.
Sign up to join this community
How are or were vias made commercially?
Wikipedia (http://en.wikipedia.org/wiki/Via_(electronics)) mentions "The hole is made conductive by electroplating, or is lined with a tube or a rivet"
Can anyone provide more details on these processes, with an eye towards replicating the process? (I realize the standard DIY way is to thread some single-core through and solder it. That seems relatively slow and not amenable to automation).
PCB production after stack up cure:
Drill the hole. This is through the solid copper (un-etched) outer layers and feature etched internal layers (for a 4+ layer board).
Copper burrs are removed in the deburring process.
Melted epoxy resin is removed by a chemical desmear process. (Without this, you cannot get good plating coverage to the internal copper.)
Clarification: This step is only on 4+ layer boards. The plating around the via top and bottom annular rings will get good conduction on a 2 layer board, even if the edges are epoxy insulated.
Sometimes (but less seen due to nasty organic chemicals needed) the resin and glass fiber is etched back to expose more of the copper layers. (Again: only on 4+ layer boards)
Around 50 microns of electro-less copper is deposited within the hole to allow electroplating.
Polymer resist is added to the board to cover everything that will be etched away (all but via pads, normal pads, traces, etc).
Around 1 mil of electroplated copper is deposited into the barrel and on every surface of the PCB not covered with resist.
Metallic resist is plated over the electroplated copper.
Polymer resist is removed.
The Etching process removes all copper not covered by metallic resist.
Metallic resist is removed.
Solder mask is applied.
Surface finish is applied (HASL, ENIG, etc.)
Some things to consider about vias and DIY via replacements. Thermal expansion is the death of PCB boards, and vias are the most abused portion.
An FR4 material is resin impregnated glass fibers. So you have a weave of fibers in the X and Y direction, covered with "Jello". The glass fibers have little CTE (Coefficient of Thermal Expansion). So the board will have maybe 12-18 ppm\C in the X and Y direction. There are no glass fibers restricting motion in the Z direction (the board thickness). So it might expand 70-80 ppm\C. Copper is only a fraction of that amount. So as the board heats up, it is tugging on the via barrel. This is where cracks will form between inner layers and the via barrel, severing the electrical connection and killing the circuit.
For a home made via, you are most likely going to have issue with the plating being thinnest in the middle of the barrel, and this area failing with temperature expansion.
One commercial alternative to plating for 2-layer prototype boards is to use rivets, such as this machine. A DIYer could either solder the rivets instead of pressing them, or fabricate suitable dies for a cheaper press if they have access to a lathe.
