2017-05-23 (Tu) Pi0 Laser Tag PiTagErrUs

Prototyping circuit boards has not been mastered yet. Inexpensive hobbyist-grade material leads to errors but that is the cost of cheap material. A series of different methods were experimented with.

In an attempt to keep the transfer paper stationary (I'm missing a good paper pun here) while it cools, masking tape was applied to each end to pull it tight across the copper face. Despite this tautness, the tape did not help with a good transfer.

Masking tape on the ends of the transfer paper

One problem created by the masking tape was the adhesive residue which wadded up while ironing. Tape strips were rearranged so it was only on the bottom of the board. In this way, the hot iron never came into contact with any tape. This eliminated the residue and the tape kept the board from slipping but the transfer result was not good.

Tape but only on the bottom of the board

When copies of the board were printed, it was advantageous to print multiple copies at once. The simplest way to do this was to duplicate the board in EasyEDA. Copy-paste. On the screen, this meant only the original board had accurate part numbers. There were six resistors on each board but the first duplicate started at seven.

The traces were copied with GIMP, a raster editing program, then printed. The full-resolution image shows the problems better. Even on straight lines, there was visible dithering which resulted in lines that would probably become unusable or at least difficult to transfer and etch.

Winning recipe
  • Set iron to high heat
  • Slide the iron across the paper
  • Do not use tape
  • Do not apply pressure while cooling

Click for full resolution

The etching solution mixed up last time was the wrong proportions. A simple calculation of the desired proportions showed that to take the 1:2 ratio and switch it to 2:1, all that was necessary was to add enough 3% hydrogen peroxide solution (H2O2) to double the amount of etchant. This was easy enough. The label on the container was moved so it lined up with the level of the existing solution.

Measuring level via label

The greenish solution was poured into an etching tray and the container was filled to the same level with 3% hydrogen peroxide solution. This was all combined in the etching tray to try on a good board.

Measuring 3% hydrogen peroxide solution

One circuit board was successfully etched but it took a long time. A green cloud could be seen near the board which indicated the etchant was working but it wasn't getting fresh etchant as it worked. A couple of servos were connected to an Arduino in at attempt to gently rock the solution while the board etched. They can be seen in the animation below happily spinning back and forth. Rocking a vat of acid unattended seemed...unwise. A more manual approach was used for the second board.

The acid bath and board were rocked back and forth by hand and monitored. Etching completed in less than ten minutes which was substantially less than a stationary tub of acid. It was nice to see that the etchant was useful.

A lesson in impracticality and unnecessary danger


The rest of the posts for this project have been arranged by date

First time here?

Completed projects from year 1 
Completed projects from year 2
Completed projects from year 3

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2017-05-20 (Sa)