March 13, 2014

   
 

Muppet
This page contains notes on my printed circuit board process.

I've recently added to my garage mess a simple setup for making my own printed circuit boards. This process is taken from instructions in the QRP-tech Yahoo group headed by Chuck Adams, K7QO. Following Chuck's instructions I was able to successfully make a small pcb 1st try. I picked out a simple circuit - a noise generator that can be used for receiver testing.

This pcb was done Dec '13.

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January 8, 2014

The next muppet pcb I have made is for experimenting with a colpitts JFET oscillator with an inductor and capacitor added to "pull" the oscillator frequency a little bit (a VXO - Variable Xtal Oscillator). The QRP-tech Yahoo group is experimenting with using the Fairchild and/or ON Semi J310 N-Channel RF amplifier. The muppet layout below may not appear to scale. If you try to use it to make a pcb make sure it's scaled to the proper size. The width is exactly 3.2" . I purchase SS pcb material in a 4 x 6 inch size and try to make all my muppets half that size. I always make an assembly drawing to use in assembling a pcb but even more important is the placing of components on the assy dwg sometimes catches pcb layout mistakes. An example of finding a layout mistake this way is illustrated below. Notice on the assy dwg the connection between the capacitors and the JFET source is drawn in as a line. That's because I accidentaly left it out. The layout at the left is after I went back and added that connection. I layed out this pcb to accomadate a nice little 10K trimpot. If you were using this circuit in a receiver you would probably want to use a front panel mounted 10K 10turn pot.Notice that the square pads that look odd are actually ground plane connections. Expresspcb allows this kind of pad to thermally isolate the pad from the large ground plane so soldering to it is much easier. Before using this layout also needs to be flipped.

 

I purchase my SS pcb material in 4" x 6" size and cut it in half giving me two 3" x 4" pcb's. Then in the layout with Expresspcb I leave 0.4" all the way around to be etched away to leave a nice looking "frame" around the outside edge of the board. . .so, my 4" wide pcb layout becomes 3.2" wide (2 x 0.4 subtracted on each side.). . .but, I still attach it to the 3" x 4" piece of material. For pcb's that are intended to be installed in some piece of equipment you don't want to have that cute little "frame" around it so that when you drill holes in the corners the metal screw can ground the pcb to the metal enclosure.

FOUND ANOTHER MISTAKE If ya use this layout you must add a jumper between the 100K resistor and the gate connection.

I got my image to print by printing from Expresspcb to a .pdf file. (If you don't have that capability on your PC you can dowload cutePDF and add that capability.) Then I open that .pdf file in photoshop, flip it and print it. If you don't have photoshop I suggest googling the phrase "free photoshop" and you'll see there are various ways to accomplish it. There are a multitude of free graphics programs plus I believe Adobe will allow you to dowload and use Photoshop CS2 for free.

(One more modification to my layout. I added a few pads so I could add some decoupling components to the drain connection if needed. Since it's such a minor thing I won't show it here.)

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How to really mess up the making of a muppet pcb: January 31, 2014

The first muppet board I made came out perfect. I followed all the instructions perfectly. But on the 2nd I got lazy. Here's the things I did wrong.

1. I chose some old pcb material that was 2oz copper instead of 1oz and it was double-sided.

2. I didn't cover the other side requiring the process to etch many times the amount of copper.

3. I did it in the garage (that's the correct place to do it) but it was 30 F outside and the etchant was cold too. Remember, heat enhances chemical processes so cold slows it down.

4. When I put it in the etchant I started stiring slowly but after a while got tired. After 30min it still wasn't completed but some of the resist had come off so here's the result.

It pays to follow instructions exactly !!! , and do it in a warm room.
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Here's another muppet problem I created: Feb 14, 2014

I thought it'd be cool to use blue pcb material instead of that ugly green. Well, as it turns out it creates a problem while you're etching the board.  The etch resist is black and the pcb material is dark blue so while you're etching it's difficult to tell the difference.  That is, when all the etching is complete the board will appear to be completely black.  It's better to use a light colored pcb material so you can see the progress while you're in the etchant. If you really want to use the blue you can use a HIGH-powered LED flashlight up close to monitor your etching progress.

It's best to follow Chuck's directions as outlined in his lab notebook. 

BTW, a link to his latest version is on his web site.

I just finished a muppet pcb for the local Oscillator (LO) for the 40-40 transceiver (xcvr)

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February 15, 2014. More mistakes. See the layout below.

Notice in the bottom left there are two ground pads that aren't connected to ground.

Now it's fixed.


The finished board. You can see a little paper still on the black toner. If you can see that it's NOT on the exposed copper it doesn't hurt anything. If there is a very thin coating of paper on the copper it will be etched away with the copper so don't worry about it.

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This is the Ugly Weekender VFO board.

OOPS! See anything wrong with the pcb above? Notice the nomenclature is backward? That's cuz I forgot to "flip" the image before making the board. Below will appear the corrected board when I get it redone.

 

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Here's another muppet board that I made a mistake with. Notice the toner did not adhere properly in places. Remembering back to the procedure to identify the mistake, I think it was in washing the board to clean the board after scrubbing it with the Scotch Brite. I used a lot of Dawn dishwashing soap and I'm pretty sure the problem came when I didn't rinse the soap off properly. I think next time I won't use soap. I mean, after all, the scrubbing with the Scotch Brite should get all my finger prints off.

Notice the pads for the resistors and capacitors are fairly close together. It allows you to use 1206 SMD parts if you want.

Here's a correct board.

. . .and, here's the final board.

Looks good !! I made it on thin, blue copper clad. the blue makes a nice looking pcb. In the etching process you have to use a high intensitiy LED flashlight to watch the process because the unetched areas are black and the pcb material is dark blue and you can't tell when the etching is finished if you don't use the light.

BTW, I timed the etching process and it took 5min. I kept on etching 'til 6min was up just to make sure. That was with me stirring the etchant continuously.