Without a doubt the solder paste dispenser is a cool tool. Compressed air hisses and solenoids crackle while precise amounts of solder paste extrude into beautiful droplets on a PCB. A few minutes with a paste dispenser saves $15-$25 (or more) on stencils, a life saver if you want to pick and place a one-off prototype. Only Akiba’s CNC milled stencils seem to beat it in speed and convenience.
Our dispenser is a random-name 986A, which seems identical to the more widely available 983A. There’s dozens of brands that all look similar, and generally use the same model number as a Hakko tool. Qwik, Best, Aoyue, Gayoue, Qinsi, Gold, the list goes on and on. Check it out in the video above, and continue reading about it below.
Last week we unboxed a load of tools shipped back from the parts market in Shenzhen. We’re assembling a mini SMD production line with a bunch of the tools we spotted in hackerspaces and workshops. While we don’t plan to produce anything for sale, we hope to learn more about manufacturing and possibly ease our prototype assembly backlog.
Over the next couple weeks we’ll demo each tool. In April it may be possible to get your own through a group buy, but we’re also scheming with Seeed Studio to make things directly available from their store.
First up is the solder paste dispenser. It’s a relatively simple tool that provides controlled bursts of air pressure to a solder paste syringe with an airtight piston.
The controlled bursts make sure that an exact amount of solder paste is released each time. It’s triggered either by holding a button mounted on the syringe, or via a foot pedal switch.
There are plenty of settings available to find the sweet spot for your mix of flux and solder. For “Mechanic Paste“, a cheap tub available on eBay for a few bucks, we’ve been using 50 psi of pressure and a 0.08s to 0.12 second dispensing time. We also use a tiny bit of vacuum to help separate the paste from the syringe, but not too much because it seems to bleed air to make the vacuum.
On the back 4 DIP switches set the dispensing mode. Some modes give 1-16 drops per button press, at an interval specified by the interval setting on the front. A continuous mode dispenses long paste snakes – maybe a good setting for laying paste for ICs.
The instruction suggest holding the syringe at a 45 degree for optimal dispensing. Then hit the button or pedal and paste shoots out according to the mode set by the DIP switches.
We tested the paste and reflow process by tossing a bunch of different sized parts on one of our QFP v2 protoboards, available at Seeed for $10. We added 0805 capacitors, 0805 chip LEDs, a 64 pin TQFP PIC16F, a button, and a USB jack. A variety of parts with different footprints and thermal mass.
Everything went into the oven for our tweaked heating profile, more on that soon. Most parts aligned properly and soldered nicely to the board. The TQFP PIC had a bunch of bridges, certainly caused by lack of experience and easily fixed with some solder wick.
Three syringes, 6 plastic nozzles, and 6 metal needles came with the dispenser. We’ve had no luck getting any gauge of needle to work well, and have settled on the mid-sized blue plastic nozzle (in use, not shown).
70 to 100PSI of oil-free, dry air is needed to push the paste out of the syringe. While the dispenser may be cheap, enduring air compressor ownership could be hazardous to your health.
We found this 6L cheap compressor that’s slightly smaller than a tower computer for around $100. 24L seems much more common, but they’re way too big for our workspace. If you get a cheap one like we did, expect lots of noise. Several commenters have suggested a second hand low-noise dentist’s compressor as an alternative.
The air should be run through a dewatering stage. We’ve ordered one but it’s not yet arrived.
The dispenser air in and air out are both connector-less press in, pull out quick releases. The compressor-side connector though is something much larger than the standard 1/4inch quick release air hose we’re familiar with.
No adapter was available locally so a hack was employed. The end of a standard air hose was tenderly chopped, then the dispenser hose gracefully epoxied inside. A dash of hose clamps for safety, and a wad of tape and bubble padding to lessen the blinding factor of the hose clamps should this ever blow apart and whip around the shop.
You can check out previous workshop videos here.