Sunday, October 24, 2021

Surface mount on home drawn circuit board

I've been slow to adopt surface mount components for home construction but watching Paul, VK3HN's, technique has convinced me it's the way to go. The way he lays components on a board, draws the tracks with a pen, then simply solders components on to the surface seems particularly elegant.

As a test I've built a simple emitter follower audio stage with a 3904 small signal NPN transistor. The transistor is tiny but able to be soldered. I've used a normal Sharpie pen in the past but recently picked up some Staedtler permanent markers which are often recommended. Here's the resist and you can see the transistor top right:

I etch with ferric chloride in a small plastic container.

This small amount has done a few boards already. It would last longer if I coloured in more of the copper area. Paul tells me that warming the solution will keep it going even longer if desired.

This board wasn't great but worked well enough to solder components in place.

A wonderful benefit of surface mount components is that you can buy these books containing all common values for not much money. I bought the large 1206 sized components to make it easier for me to work with them. It's great to have plenty of every value resistor and capacitor at hand in a compact book. The result, on my first attempt, is a bit rough:

Working with surface mount is not hard if you have good light, a magnified headset, tweezers, and something to hold down the part while you solder the first connection to a component.

1 comment:

Unknown said...

Great job Peter! A couple of thoughts.

Warming the FeCl3 solution by floating the etch container in a basin of hot water decreases etch time significantly. Maybe twice as fast. Rock the etch tub to keep the FeCl3 washing back and forth over the board. Don't stop! If you stop, the reaction slows and the board can become coated in residue in places.

Note that warming the FeCl3 does not lengthen its usable life.

Second thought, you've etched a huge amount of copper off unnecessarily. That just uses up your FeCl3 and you lose the opportunity to create a useful ground plane. Which can also be used to build paddy board or ugly using leaded parts, if you ever need to.

Do the fine traces just as you've done. Then get a regular Sharpie permanent marker and colour in all the blank space, right up to a 3mm away from your outermost traces. Connect this plane to ground. This won't make much difference at audio or slow digital but may be the difference between stability and oscillation at RF.

Looking forward to your next PCB.

Paul VK3HN.