Monday, April 19, 2010

Finishing up the PCB

Finishing the boards what i did was:

Drilled the holes.

The Last time I tried to drill a board I used up the entire kit of bits I got on eBay, using a genuine Dremel tool in an expensive genuine Dremel drill stand. The Dremel screws into the stand and it must have not been as perpendicular as it looked. Most of the bits broke just as the drill went through the board completely. Too much flex - plus the Dremel sounds way too much like a dentist drill for me to like them much. I had even purchased a regular looking chuck adapter that didn't help matters any. Not recommended.

Since then I got a real drill press at Harbor Freight - I got it for around $50 on sale - Nice bench top unit I have used quite a bit for regular sized projects. I figured that the bits had 1/8" ends , so I mounted up the bits, set the speed as high as it would go, and drilled all 64 holes without one broken bit. Considering I spent less on the big drill press than I did on the Dremel tool, I can't recommend the bench top unit enough. Plus while I was there I spied a grab bag of small drill bits and picked up a set that I used this time.

Tinned the traces.

I was initially to intimated to try surface mount soldering, looking at the Sparkfun tutorials and then actually doing it is sometimes very different.

For those of you out there contemplating it here are a few tips. Especially if you made you own board and it's gleaming copper traces are staring you in the face.

Buy one of the flux pens. I initially put a little dot of solder on each pad to solder down the chip, however when i tried to get it aligned these little dots got in the way - the pins wanted to fall to either side. I tried to get the solder bump a little smaller, but the iron wouldn't pick up as much as I needed - then the little over the head light bulb went on and I just covered all the traces liberally with the flux (you may need to push the pen down a few time to get fresh flux flowing I did). Then all I had to do was was drag the soldering iron along each trace, trailing a small blob of solder and leaving a nice thin coating of solder. Only once in a while did i need to refresh the blob of solder on the tip of the iron.

I brushed the Flux pen over the pads again for a fresh coat. Then I heated one of the corner pins, dropped the chip down on it, checked to see that it was stuck, and did the same to the other corner of the chip. After that it was just a matter of touching the iron to each pin , and inspecting after all were touched - they all had a little meniscus of solder from the IC pins to the pads. Touching with a pin I tested each to see that they were well and truly stuck.

I have to mention the soldering station I got. A Weller WES51 Analog Soldering Station, Power Unit, Soldering Pencil, Stand and Sponge. The analog is quite sufficient, who cares if it is 600 or 611 degrees, I don't. It is a absolute joy to use, and one of its best features is that it turns itself off after no use in 99? minutes. It cost close to $100 on sale at Amazon. As they say - you remember the quality long after you forget the price. Highly recommended.

Cutting the baoards.

Well i could have done it many ways, as soon as I get a real paper cutter I will try one of those, but I have a scroll saw, and it does the job quite nicely. Wish they made saw blades designed for cutting FR4 for the saw.

Lessons learned and notes for next time

  1. Use real tools - drill press and soldering station.
  2. Hook up a the hose from vacuum to the drill press to catch the drill dust.
  3. Look for real paper cutter at the yard sales.
  4. Get a new prescription for the glasses I use in the shop, all these tiny precision tools, parts and soldering gives one a headache.