Polyurethane protecting PCBs

PCB

What you see above is a home-made PCB. No, this isn’t an example of a terrible toner transfer job, but rather evidence of the ravages of time. This board is seven years old, and the corrosion and broken traces show it. Luckily, [George] already has seven years of environmental data for a cheap DIY soldermask.

Seven years ago, [George] took a piece of copper clad board, masked half of it off, and sprayed it with fast drying polyurethane. After drying, he put it on a shelf in his garage. The results were fairly surprising – the uncovered portion is covered in verdigris, while the coated half is still shiny and new.

[George] took this a bit further and experimented with other spray can coverings. He found Testors spray enable worked just like the polyurethane, burning off when the heat of a soldering iron was applied, and also passed for a professional PCB.

Put a solder mask on those homebrew PCBs

While making your own PCBs at home is one of the best marks of a competent builder, if you want to give your project a more professional vibe, you’re going to need to do better than bare copper traces on a piece of fiberglass. To help out his fellow makers, [Chris] sent in his Instructable on creating a solder mask for homemade circuit boards using a minimal amount of tools and materials easily sourced from the Internet.

[Chris]‘ soldermasks are made from UV curing paints he found on eBay. Of course the traditional green paint is available, along with paints very similar to the Sparkfun red or Arduino blue soldermasks.

After brushing the soldermask paint onto his home-etched circuit board, [Chris] printed out the solder mask onto a piece of transparency film using a laser printer. This mask is vitally important if you ever plan to solder your board; by covering the pads you wish to solder, the paint won’t cure and can later be removed.

[Chris] cured his soldermask by leaving it in the sun for a half hour. After the paint was dry, he removed the excess paint covering the pads with a little bit of turpentine and some elbow grease.

While [Chris]‘ paint had somewhat of an ugly matte finish, the soldermask does its job, protecting the PCB traces while leaving the pads uncovered and ready to solder.

Kapton tape aids in drag soldering surface mount parts

Drag soldering works exactly as its name implies, by dragging a bead of solder across fine-pitch pins you can quickly solder an entire row. The method relies on clean joints, so liquid solder flux is often used to make sure there is good flow. But if you’re drag soldering on boards that you’ve etched yourself the solder can sometimes run down the trace, rather than staying where you want it. Professionally manufactured boards don’t have this problem since they have solder mask covering the copper that doesn’t need soldering. [Ahmad Tabbouch] has a method that uses Kapton tape to act as a temporary solder mask on diy boards.

The process involves several steps. First, three strips are place horizontally across the board, leaving just a portion of the upper and lower pads exposed. Those pads are then tinned with solder, and a light touch with an X-acto knife is then used to score the tape covering the vertical rows of pads. Once the waste as been removed, two more strips are added and those rows are tinned. From there the chip is placed and soldered as we’ve seen before; first tacked in place, then fluxed, and finally drag soldered to complete the connections. This achieves a crisp and clean connection, presumably without the need to clean up your solder mess with solder wick.

Kapton tape resists heat, making it perfect for this process. We’ve also seen it used on hot beds for 3D printers, and as a smoothing surface for sliding mechanisms.

[via Dangerous Prototypes]