Friday, September 7, 2012

It's HERE! It's HERE!

My local FedEx depot isn't far from where I'm working, so I went over after work last night to pick up my package. As with the last order I placed with PCB-Pool, the boards were shrink-wrapped to a stiffening card and packaged in a very sturdy cardboard box. This avoids problems with damage enroute. I'd also ordered the stainless steel solder paste stencils and they were taped securely to the stiffening card.

To avoid having to rush the production of a replacement board if one turns up defective, a board house may choose to make extra copies of a board. Normally these are discarded, but one of the PCB-Pool options is to agree to buy these extra boards at half price. I'm sure that keeps their overhead costs down and is a benefit if you can make use of extra boards.

In my case, this is the first time I've attempted to build something so dense, or with this many components. It's also the first time I've had hot air soldering equipment available, and there's a reasonable chance I could damage the board. I decided to agree to buy one extra board, if they made an extra. They did, and both passed the electrical test, so I have two boards.

Whenever I make a PCB, I worry that I'm going to get the holes too small or pads the wrong size, and I'll end up with an expensive piece of trash. The evening I placed the order I found that the holes for the connector pins specified in the Eagle library would be a very tight fit. I understand this would be good for a production run where you don't want the connector to rattle around and get out of alignment, but not so good for a hobbyist. To avoid a potential problem I made the holes bigger. I know from experience that this connector will fit nicely in an 0.042" hole so that's what I specified, but since PCB-Pool uses metric drills the holes are probably even bigger than that. Practically the first thing I did after ooohing and aaaahing over the boards was to fit the connectors into the holes. A loose fit, but far better than the alternative. Maybe I'll tighten it up a bit on the next boards. Or not.

My next concern was the shape, size, and positioning of the components on the top of the board. Here's a photo taken through my microscope, showing two SOT-23s pretending to be FDV301s, a real BSS83, and an 0603 resistor sitting on the board. They're all slightly out of alignment -- I must have bumped the board while I was fiddling with the camera -- but it looks like everything fits right. I still think there will be room for me to get my soldering iron between the components, but I don't think I'd want to make things more dense.

In case you're wondering, those are 8 mil (~0.2mm) tracks with 12 mil (~0.3mm) vias. You'll also note that I've placed the vias within the component pads, rather than separate. This allows for a denser layout, but I understand it can cause problems with solder starvation when doing production reflow soldering. Since my problem is usually too much solder, that doesn't worry me. The next couple of days will show whether it should.

If you click on the picture to enlarge it, you may be able to see the divot in each pad. That's the mark made by the electrical test machine, as it probes each pad to verify electrical connectivity.

So the boards look great. I have all the parts, and they appear to fit properly. The only question now is what the hell was I thinking? There are 585 parts on this frelling board, and three and a half more equally-dense boards yet to come. It'll take weeks just to get all the parts soldered down, longer if you count the testing I need to do along the way. I'll be at this for a year.

It's insanity.

Hence the name of this blog.

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