UFE Board Assembly Progress
Posted by retromaster on September 18, 2009
The pictures above show the UFE board with quite a few components (including the PIC32) assembled, and the PIC32 being recognized by Microchip’s PicKit2 programmer. I haven’t tested actually programming the PIC32 (since I do not have any appropriate binary to program it with), but I do not anticipate any problems at this stage. I’ll go on with assembling the rest of the components (possibly with the exception of the SDRAM, which I’ll leave for later). I might try writing a few lines of test code to blink a few LEDs I’ll connect to the LCD daughterboard connector. Soon, I plan to move on to building the LCD daughterboard.
While the UFE board seems to work fine at this point, the looks of it leave much to be desired. I used the old trick of painting the board with rosin-based flux and drying it. Once dried, it is no longer conductive (and sticky), and it protects the board from corrosion rather well and obviously, you can solder through it. The problem is that I prefer using the solder-and-wick method for SMD chips, and that results in a mess (that you can see in the picture above) that you cannot clean (otherwise you’ll remove the protective flux layer as well).
So, it would be great if I could apply a soldermask on my PCBs. Now, I know that it is possible to use UV-cured inks or films for the soldermask application. But they are somewhat difficult to obtain for me, and I am quite used to the toner transfer method and I am reluctant to add a radically-different step. While looking for an alternative on the net, I came across some great results obtained by using heat-curable Pebeo Vitrea paint as a soldermask (masked using toner).
Basically the glass-paint soldermask method works like this: 1. The PCB solder image is applied on the etched PCB using regular toner transfer. 2. The PCB is painted using the Pebeo Vitrea paint and cured. 3. The toner gets in between the PCB and the paint, preventing adhesion of the paint and effectively masking the areas to be soldered. 4. Removing the toner using acetone leaves the solder areas with bare copper and the rest of the paint intact.
I’ll experiment with this method while building the UFE LCD daughterboard and post the results. Hopefully, I’ll be able to obtain the Pebeo Vitrea around here, but otherwise, I guess other kinds of heat-curable glass paint might work.