Not every board needs to be assembled with a pick and place machine. Especially for those working in a lean startup environment, PCB assembly can be costly and slow. Even with smaller, highly populated SMT boards, one can save money and time by soldering them yourself. Believe me, even the larger firms will appreciate you saving upwards of $5K or 2 weeks lead time when assembling a prototype.
I would like to share a formula for determining if your board should be sent for assembly or soldered yourself. I will also cover some basic equipment and some techniques.
I am going to assume that you know how to solder SMT components, QFN or DFN packages and at least 0603 resistors.
If you can solder smaller packages, and are comfortable with BGA, then all the power to you!
Here is a basic formula that can help you decide whether to send out a board or keep it in house:
If your COSTtotal is less than your PCBA quote, then you have an opportunity to save you or your company some cold hard cash. Also, another advantage of an in house assembly process is that it is almost always quicker for you to assemble your board yourself. Of course if the board is needed quickly (<5 days), you may be hard pressed to find a manufacturer that can meet that deadline. Assembling your board yourself may be the only option.
Undertaking on an in house PCBA assembly requires a bit of equipment and a few tools to do it effectively:
- I use the following products when organizing my BOM for soldering. It has worked well for me over my 8 year soldering/hardware design career.
By placing components into these smaller containers, and storing them in the larger ones, I can keep an assembly project organized, protected from ESD, and I can quickly pop the lid of each container with my tweezers and grab the part. All of my boards are labeled with reference designators. I print out a simple spreadsheet, ordered alphabetically by reference designators and their corresponding values. I keep the printout at eye level while assembling my board, quickly scanning it to see what value I need, and then going to my organized containers to grab the right part. This set up usually takes a bit of time to set up (an hour for the picture below), as every component needs to be unpackaged and labeled. However the time savings are huge when it comes to populating your board. You really don’t want to be stuck with 50 individual plastic bags, with all of your parts still on reels.
- A well equipped solder station with a temperature controlled solder iron with micro-soldering tips.
- Solder wick
- Solder tip cleaner, I prefer wired over sponge
- Tip tinner
- Solder paste
- Rosin flux core solder, fine gauge
- Heat resistant anti-static mat
- Fume extractor (important!)
- Anti-static tweezers
- Continuity tester
You will notice that the bare minimum equipment list does not include stencils or a reflow oven. With a little bit of practice, you can solder all SMT components with a solder paste syringe, soldering iron and a heat gun.
PCB assembly is an important skill for any hardware designer. However, knowing when to do it yourself and when to outsource is an equally important skill. Note: sometimes it might be cheaper for you to assembly in-house, but it may not be the best choice if you have other pressing tasks and projects on your plate. Use common sense, basic math, and you'll probably make the right decision.
About the Author
Brien G. East Jr. is the Director of Hardware Design at Blue Clover Devices. A Canadian expat, Brien is happy to embrace sunny California as his new home.
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