Manufacturing boards using surface mount and a hot plate

I thought I’d write a little note and post some pictures of how I’m assembling the LCD display boards. The PCBs are manufactured at Seeedstudio and are really nice quality. I’ve tried to use as many surface mount components as possible, but have some through-hole also (headers etc). The LCD itself is also surface-mount, but I solder it on manually, not using the hot plate.

I basically use solder paste in a syringe and manually apply solder paste on each surface mount point.  It would probably have been slightly faster using a surface mount stencil, but using a syringe is also quite quick and not as messy as a stencil.

I then place the surface mount components onto the paste. In my case these are just simple capacitors and resistors, so it’s not very complicated. I used 1206 size originally, but have now started using 0805 size capacitors.

The board is now ready to be fried. There are several ways of doing this. Some people use a reflow oven that surrounds the entire board with heat, but I find that if the surface mount components are only on one side, using a hot plate such as this is the easiest. Not sure what the pros and cons are of each, but Sparkfun have also recommended using hot plates. I use a thermistor to control the heat, but since my hot plate has a thermostat I just use the thermistor to guide me towards the best setting.

Here’s a picture of some of the boards on the hot plate. I can do several at the same time.

The whole process of applying paste, heating them on the hot plate and then manually soldering on the LCD means I use about 1 hour on 10 boards. Of this, just doing the surface mount takes maybe 10-15 minutes for 10 boards. It’s definitely faster than manual soldering.  I might get more efficient as I move along. Right now I’m also soldering on headers on all the boards as it makes it easier to test, but I won’t do that in the long run. I’m shipping 14 boards to the store tomorrow. I will keep a few to sell here on the site. Unfortunately, Arrow have told me the remaining batch of 222 LCDs is delayed until July, so if you want to test a board early, it might be good to get one of this first batch.

Here’s a zoomed in picture of one of the boards, before the solder paste has melted. The picture also shows my silk-screen error (P1.4 is really P2.0). Other than that and a slightly inefficient LED-connection, the first batch of boards seem to be pretty ok (the points that need to be connected to turn on the backlight are a bit far apart, but no big issue). The next version will also have the SMT components on the bottom, as it looks nicer.

And here’s a picture of the LCD connector soldered onto the board. I do this manually, but it’s pretty easy when using flux to ‘guide the solder’. You can barely see the liquid flux on the board around the connector.

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