In preparation for my Arduino-based AVR HV Programmer boards coming back, I decided to step up my home lab surface mount soldering capabilities.
Step one was to find a cheap stereo zoom microscope on ebay, with 7-32X magnification, perfect for working on surface mount devices. One of my biggest frustrations in the past is that with a cheap magnifying ring light, I can’t actually see what I’m working on – not any more! I’ll post some photos of the microscope when it comes.
Step two was to build a soldering hotplate. I like using a hotplate for surface mount soldering because you can actually watch the board as the solder paste reflows, and manually add/remove/nudge components around with a set of tweezers. This is great for engineering work where you may still be making component changes and other tweaks to the board. Mass production is probably best left to a reflow (aka toaster) oven.
The heater is a 1/2″ 500W, 120VAC cartridge heater I bought from McMaster-Carr for about $25. The hotplate itself is a 3x4x1″ chunk of aluminum that I machined with a carefully sized hole just below the center for the heater to slip into, as shown. A type-K thermocouple (top right) measures the temperature and provides a signal to the controller. Ceramic standoffs insulate the hotplate from the bottom aluminum baseplate. For safety, there is also a ground strap, shown on the bottom right.
This the second PID controlled project I have done, the first was my PID Controlled Solder Paste Fridge.
The controller box contains an Omega CN77000 series PID controller and an IR/Crydom 240V 40A (overkill!) D2440 Solid State Relay (SSR), along with a power switch, fuse, and power connector. The PID controller and solid state relay were both found at a now-defunct Silicon Valley surplus store for a few bucks each. A 3′ umbilical cable connects the controller to the hotplate.
60/40 leaded solder reflows at about 185C, and lead-free solder is around 200-230C depending on the alloy. (Wikipedia has a good list of reflow temperatures.) The hotplate can easily reach these within a minute or two from room temperature and could get much hotter if necessary.
It can also be used to cure epoxy and perform any other tasks that require a precisely controlled heater – this could be the world’s most overengineered coffee warmer, if not for the dangers of lead poisioning.
Update: I just posted some more information about the microscope.