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Oct
12
Written by:
Gary Holbrook
10/12/2008 5:24 PM
When we last left our hero (yeah, that's me), he was about to try his luck with a second two layer board after his initial failure...
I did. And I failed. Again. The board still didn't etch cleanly the second time around, but it was better. In fact, it was "good enough". Using a very tiny screwdriver, I separated the many traces that did not etch properly. That time consuming process was followed by a very careful testing process, so that I would know precisely how poorly the etching job was. Finally, after lowering my expectations to simply being able to "talk" to the chip, I attached it to the board.
This is a $17 chip, and etching a double sided, high density board is a pain in the rear. You might imagine what I was saying to myself as I soldered the chip onto the board. It was something to the effect of "Don't screw up. Don't screw up. Check your alignment. Check your orientation."
The programmer couldn't talk to the chip. Nothing. Nada. I busted out the eye loupe and checked my solder job. Solid. The failure seemed so peculiar, but I kept checking things with my multimeter. Finally I realized the problem. The chip was oriented 90 degrees the wrong direction. You can imagine my choice language. Unfortunately, the desoldering process toasted the board. Those tiny traces don't do well with multiple heat cycles.
School started up so my time has been short. Also, I won't lie, I haven't been eager to get back to failing again! This last two weeks have been really stressful, and I needed to get in touch with doing something I really love doing...like making boards.
Before starting, I got a pair of cotton gloves. My developer solution was looking a bit dark, so I changed it out for fresh solution. I decided to use my smaller piece of glass for exposing the board, so the glass wouldn't flex as much. If the mask isn't absolutely flat, it may produce blurry results. Finally, I printed the mask out on our inkjet printer...using the "heavy" ink setting. I love that printer. The ink took a long time to dry (I gave it two hours after smearing the first mask). When I handled the exposure glass and the masks, I used the gloves. Finally, after drilling the registration holes, I exposed the bottom side first because it's lower density. Any light leaking around the bottom when I exposed the top would be less likely to damage the exposure. When I got ready to expose the board, I turned off even more lights than usual.
Usually, this degree of caution is superfluous...but this little board is so tiny that every bit counts. That was the case this time, too. The initial results looked good, and I bragged to Aimee that it was perfect. After getting a good look at the board through an eye loupe...I had to agree with myself. It was perfect!
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