BUILDING REFLOW HOT PLATE
One method of soldering surface mount parts onto PCBs makes use of a hot air gun, but that method works much better if the entire PCB is heated to nearly the melting point of solder with a hot plate, then the hot air is directed surgically to flow solder just where it is desired.
I came across an open source design for a soldering plate which I decided to build. This one is not very large but will be adequate to my needs since I also have a reflow oven for larger PCBs. I sent the gerber files off to the fab and recently the finished boards arrived at my doorstep.
The project stated that it had a bill of materials, which wasn't quite as user friendly as it initially sounded. That is because almost every component was listed as a part number for a supplier in China, not a distributor where I could order it here. Worse, the essential details weren't listed in the BOM, for example it simply listed a part as 'diode'.
I looked up the parts pages (in Chinese) on the supplier site and tried to puzzle out the specifications sufficient to source it from western sites. I was able to do so, I believe, although the final proof will only come when it is operational in the next day or two.
The particular gerber files produced a silkscreen with many pads labeled 'TC', other places where I had somewhat redundant names LR1, TR1, PR1 and so forth for resistor locations. The worst issue was when I began assembly, where the pad sizes were wildly different from the actual part listed.
A set of 10nf capacitors were listed as 0403 size in the BOM but when I was ready to solder them down, I found the pads were for 1206 parts. There was too much of a gap between the copper to ever get an 0403 part soldered down. Fortunately I had a supply of slightly small 0805 capacitors of the same specification, which with a bit of care could be put into the oversized space on the board.
A voltage regulator was similarly misidentified in the BOM and was smaller than the pad layout. Again, I was able with some care and technique to get it to bond to the pads. The remaining issue which puzzles me is the third diode listed in the BOM, and shown on the schematic, but nowhere to be found on the PCB. I can improvise its placement but it is frustrating that to have to deal with so many errors.
One element of the design is the use of an ATMEL 328 microprocessor, said part currently out of stock due to overwhelming demand. However, someone gave me a handy tip - there are Arduino nano clones from China that cost only a few dollars that contain the microprocessor on the board. A few minutes with the heat gun and I had a chip ready to install.
I completed almost all the surface mount parts, having just 2 resistors and three diodes left to mount, after which there are switches, a temp sensor, the OLED panel and some miscellaneous hardware to go. I anticipate being ready to test this out on the bench, flash the processor with the control code and then give it a full test to temperature.
WAITING FOR ITEMS FOR 1130 EXTENDER AND IOB6120
I will be assembling an acrylic mount and shield for the main connector fitting into the new 1130 extender case. The glue arrived today and the plastic should come tomorrow. I bought a used jigsaw and did some metal work already for the power supply mount, thus I can wrap up all the mechanical aspects when the parts are all in.
The IOB6120 needs a header to be installed on the SBC6120 front panel, with the parts coming in the next few days. Once that is ready I can test out my enhanced PDP/8 replica.
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