Wednesday, April 2, 2014

Ferric Chlroide - with Gremlins

While (still) waiting for my replacement order of Toner Transfer Paper, so that I can continue my Minimal Project, I used some (more) small cut-up scraps for this (yet another) project. Sounds familiar, see previous post.

My Minima Transceiver VFO Module is small and will require very little Transfer Paper, which is ALL that I currently have.

Here is the Si570 VFO layout that I will use. There are vias to traces on the backside.

Minina VFO Layout
(Modified with Output Transformer)
The circuit is a little different than originally published by Farhan. Because I want to use this Module for the Minima, and as a generic Test Bench Oscillator, I included an output transformer on the board to isolate the RF Ground from the DC/circuit ground. The transformer will have a turns ratio of 1:1 and the same turn count as the transformer on the RF Mixer.

With the last scraps of Toner Transfer Paper that I have, I proceeded to transfer and etch the first side of the board. The results looked good with excellent resolution.

The backside Transfer was prepared and lined up with "great care" as to ensure the through-holes and vias would align correctly. I "now" always "Check" and "Re-check" the rotation of the board, because I have, in the past, printed the backside 180 degrees wrong.

Because you can not see through the board at this stage, other image clues are necessary for proper orientation and alignment. Tape on one edge of the PCB is used to maintain alignment while going through the Laminator the first time. After several passes through the Laminator, I dropped the sandwich into hot water to remove the Transfer Backing Paper. Checking it revealed a nice high resolution backside image. It is now ready for the Ferric Chloride Etch.

But, Now for the problem:

About 5 minutes later, when the PCB came out of the etch, I could NOT see through the hole images. DANG, the image on the backside is 180 degrees wrong, AGAIN !

But, I had carefully; checked, re-checked and aligned the image.

So now, I have come to the conclusion that my 35 year old Ferric Chloride Etch has "gremlins" that rotates the image while I am not looking. What else could it be?

This is the third, or forth, time this has happened in the last six months. (I must be just getting old?)

So, now back to waiting for more Transfer Paper.

(Anyone need a well Etched, High Resolution, but useless, I2C Si570 VFO PCB?)

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2 comments:

Jeff Whitlatch said...

How much wiring is on the back? Could you just hand wire that bit?

Eldon R. Brown SR said...

Jeff, thanks for the comment.

Yes, for this project I think there are only a few backside traces and therefore using jumper wire could have be an option.

But, I am really just honing my skills for other Homebrew and more complex projects, where many more backside trace are necessary, and a backside ground plane is desirable.

I am getting better (at least acceptable) at drilling and installing 40 mil pads, with 15 mil holes used for vias. These vias would be the same size as I would request from a PCB Manufacture, and therefore no changes are necessary when sent for Manufactured boards.

At on time I would have NOT considered attempting to build a Double-Sided Homebrew PCB, but now it's a piece of cake :-)

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