THROUGH-HOLE PLATING problem

Question

I'm making a stm32 board at home. How can I plate through holes low cost at home? Is there a low cost through hole plating kit?

Have you considered push-in plated “cylinders” for the very purpose? They have a specific name but I forgot. — winny, Sep 09 '18 at 18:17
Have a look at : https://electronics.stackexchange.com/q/70076/152903 — Solar Mike, Sep 09 '18 at 18:18
What is your sense of "low cost"? Also, STM32 packaging in biggest case still has 0.65 mm pitch, with 0.25 mm gap between pads. Are you sure you can fabricate anything like that "at home" (unless you use an expensive CNC)? — Ale..chenski, Sep 09 '18 at 18:19
Making a layout, gerbers and getting a PCB fabbed in China is cheaper than etching it at home. — Lior Bilia, Sep 13 '18 at 16:07

score 2 · Answer 1 · answered Sep 09 '18 at 18:23

What you ask is difficult to do. You could use a wire in each "via" that is explicitly soldered to the top and bottom layers. A long time ago once I saw some rivet-like things for this purpose, but I haven't seen or heard of them since.

However, today are so many cheap PCB fab services out there. Some even cater to hobbyists. That way you also get solder mask and silk screen. Trying to do this yourself is just silly, unless you value your time at pennies/hour, and don't value quality much.

score 1 · Accepted Answer · answered Sep 09 '18 at 19:00

Olin Lathrop has mentioned the only likely solution. The pieces are essentially hollow copper rivets with very thin walls. The holes are drilled oversize, the rivets inserted and then flared by striking a punch (very carefully). As you might expect, this is not exactly practical for a board with more than a dozen or two holes.

There is a chemical approach, such as is discussed here and there is a Youtube video you can find. Essentially, you dip the predrilled board into a solution which coats the board. The board and solution are then baked and the solution pyrolizes and leaves nanoparticles of copper in the hole walls (and over the entire board. The pyrolosis products get washed away, and electroplating is used to thicken the plating in the holes. Resist is then applied and etched.

Two problems: first (and least) is drilling/registering the holes. You can apply a marking system, drill, and then remove the marking for the electroplating step. The problem comes when you attempt to lay down resist on the plated hole pattern, and getting the pads perfectly registered over any sort of board size can be a real challenge. And drilling the holes requires sharp carbide tips - ragged hole walls and edges will not work.

But that's the small problem. If you're in the US, the big problem is that the active ingredient, calcium hypophosphite, is a Level I controlled substance. That doesn't mean you can't buy it - you can, it's even on eBay. Thing is, it requires careful attention to paperwork. And just ordering it on eBay from China may work, or you may get a knock on the door and find yourself in big, big trouble. Can you say "meth lab"? I knew you could. So can the Feds. At the least, unless you are a certified researcher you will have an uphill battle establishing your need for the stuff.

THROUGH-HOLE PLATING problem

2 Answers2