Paste applied (high res)
Fri April 8 2016
The stencil arrived. Today is Assembly Day!
My solder paste has been sitting in an unplugged refrigerator for almost two years and the flux has separated out, I hope it is still usable. I powered up the mini-fridge and the warmer, put the larger tub of paste in the cooler and the smaller tub in the warmer. I will let it warm up to about 105F (40.6C) and see if I can mix the flux back into it. I will try applying it to the first board; if I run into any problems I will order a fresh tub of solder paste. (See {THREAD_LINK:1022}) I have only 5 boards so I my budget for wasting boards is very tight.
The ChipQuik site says the shelf life of the solder paste is 2 years under ideal conditions (refrigerated). The flux immediately begins oxidizing the solder and after a while the flux will separate and the solder will become an unusable solid hunk. This appears to have happened with my paste. I ordered a new tub of paste (and a manual vacuum pick-up tool set) for overnight delivery. It should arrive on Monday.
In the meantime, I will continue with my plan to warm the old solder. It may work, probably not.
It is always something...
16:00> The solder paste is pliable after warming up, enough that I think it worth trying to apply it to a board. There is quite a bit that needs to be done before I apply any paste. In the meantime, I lowered the temperature on the warmer to 41C and returned the tub.
First I need to build another paper board with all the components. The machine is still loaded, it is just a matter of running through the "learn pick" for all the components and then a production run.
I need to test the reflow oven, make sure it still works.
17:00> I hit a snag with the TC33X adjustable pots. The pick angle was off by 180. I was misled when the "Train Image" window outlined the part in green even though it was rotated. I had assumed that the machine had recognized the part as rotated and would correct the orientation before placing it. Instead, the machine rejected the pick and aborted the production run. This was fixed by changing the pick angle in "Learn Pick". The next production run went flawlessly.
17:07> I am recovering the A3967's and TC33X's from the paper board and replacing them to the tray feeder. The rest of the components are picked off the board with tweezers and thrown away.
18:22> I reaquainted myself with the reflow oven. (See {THREAD_LINK:1414}) It is working, at least as well as it ever did. It is time to apply the solder paste. I need to find a solder squeegee...
18:30> Aha! I found one in a box of discarded Blink blanks.
19:00> The stencil worked well and the solder paste looked good during the pre-production visual inspection. The parts placed without any problems and looked good during the post-production visual inspection. The board is now in the oven...
I forgot to tape over the mounting holes. Not a disaster, just wasted a bit of paste and gunked up the board around the holes.
19:20> The board is out of the oven and it looks good.
There is some spalling, but that is probably due to the old solder paste.
The next step is to hand solder the through-hole parts: the headers to mate with the LaunchPad, the motor connectors, and the 12VDC power posts. I need to refresh my memory on the LaunchPad and motor connections before I solder something in backwards or the wrong part.
Everything is looking good so far, but the real proof will be when I connect the LaunchPad and apply power. I need to stop for today, leave the final assembly and test for tomorrow. There is some clean up to do tonight, cleaning the excess solder paste from the stencil and squeegee, and shutting down all the equipment in the workshop.
