LED lamp, PC board design, soldering stuff

I’d been working on the LED lamp design. I have the circuit design basically done, and I’ve been spending my free time in the past week learning Eagle CAD and designing the board. It’s quite a learning curve, but I’m also satisfied that this software can do what I need.

Here is my first board design that was good enough to try making:
led touch lamp - final board layout

I spent all Sunday afternoon working on the toner-transfer method of PC board fabrication, both for reasons of cost and turnaround time. If I were making boards in some quantity greater than one, there are several places that offer great service and prices, but for this, I’m aiming to do a simple etched board, no silk-screening, etc.

In essence, what you do in the toner-transfer process is print a mirror image of the copper traces you want with a laser printer onto glossy paper or special plastic film (I’m using the Press and Peel Blue), then you iron it onto clean copper-clad board so that it sticks, and peel away the film. This leaves behind a layer of toner on the board, which then you etch in an acid (ferric chloride solution), but the toner acts as a resist, preventing the acid from eating all the copper away. Then you wipe away the toner with acetone. (Recommended disposal of the used etchant is by neutralizing with sodium carbonate, precipitating out all the metal ions — copper is not too good for some aquatic life, so it’s preferred that it’s not dumped in the sewer — also, ferric chloride can cause damage to metals, including stainless steel sinks.)

This leaves you with something like:
LED Touch Lamp - Etched circuit board

I still need to work on a little bit of the technique. A couple places the toner didn’t adhere perfectly, and I have a break in a trace. Both I could jumper around, but I’d like to avoid that. Searching the web, I see other people suggest that you don’t want the plastic film extending beyond the board, because it will warp from the heat — I noticed this. I may try some other improvements, even up to buying a “dry” iron that has a flat surface on the bottom (no holes for steam).

About a week ago, I was soldering some parts onto the 9090 boards I bought a couple years back, intent on finally building that, when the cheap iron (the most basic 12W Weller model, non-replaceable tip and heater) I was using FELL APART. The tip just fell out. This was what finally drove me to go and buy a decent temperature controlled soldering station. All-Spec had the Hakko 936 on sale, and everything I read suggested it was a decent soldering station. So, I bought that and a bunch of stuff to make SMT soldering easier: .015″ 63/37 solder, flux pen (got both with RMA flux), a small tip, a really small tip, and some desoldering braid (Chem-Wik). I also noticed that some people seem to like these replacements for the traditional soldering sponge, like the Hakko 599B, so I picked one up. Well, I got my order today and played with stuff, and the waterless tip cleaning stuff really works nicely!

I played with the board I etched a little — while I’m still waiting for my parts order, I figured I’d solder the wires that attach to the board, just to test things out. This is where I learned that 16 mil clearances around the pads is just not going to work. I couldn’t un-bridge the solder bridge I made with repeated application of desoldering braid. So, I’m redesigning the board, for at least 24 mil around pads, maybe even more. I think though, that that particular place was even smaller than 16 mil, due to poor toner transfer.

Just in the little time I’ve looked into redesigning the board this evening, I have learned that Eagle lets you set different nets to different “classes” which have their own width and clearance values. So, for example, I can make signal traces smaller than power traces, easily. But, now, it’s time to sleep.

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