The new year is here and many of you will be coming up with prototypes that need to be sent off for assembly. There are probably even some new year’s resolutions in there to finally get a piece of hardware into production, but the hurdle of getting your first job done can be daunting. Here are my top eight pieces of PCB assembly advice for the coming year.
1. Before you even start component selection, give thought to the design scale.
What’s more important, board size, cost, or time to layout? A large board will be easier to route, but will cost more for the fab. A smaller board will cost less for the fab in terms of square inches, but may cost more due to extra layers, and may take longer to layout.
2. Factor in the cost of component size.
For passives, roughly 0603 size parts will probably be the sweet spot in terms of lowest cost. The 0603 is also a good size for overall handling. My company Screaming Circuits will assemble down to 0201 parts, but not all manufacturers will. 0603s are also easy to rework, and are manageable if you feel the need to hand solder a few.
3. Check out any exotic or very new parts.
Some parts, these days, are only available in super small wafer scale BGA, or small QFN form factors. Take a look at your integrated circuits and make sure they come in packages that you’re comfortable working with.
4. Check for sole-source parts, or low-availability parts.
The last thing you want is a completed design that’s sitting around waiting for one long-lead time, sole-sourced part. If a sole-sourced part is at risk for availability, you might want to find something similar and more widely available.
5. Don’t forget manufacturing thermal concerns when laying out your board.
Very large parts next to very small parts can cause problems. The large parts will act a bit like a heat sink and may prevent the solder for the small part from melting properly. The same thing can happen with internal copper planes that overlap on half of a small part, but not the other.
6. Give extra care to the clarity of reference designators and polarity markings.
Make sure that it’s very clear which designator goes with which part, and that there isn’t any ambiguity in polarity markings. Take special care with LEDs, as manufacturers sometimes swap polarity markings between the anode and cathode – yes, the exact same mark can mean anode on one LED and cathode on another. Also, do your best to keep reference designators off of vias or any other spots that might break up the text.
7. When you’re ready to send your project our to be built, give your files a double check.
Make sure you have the correct versions. Bills of materials are especially susceptible to having bits of information out of date that might cause delays.
8. If you’re sending in a parts kit, double check that you have all of the parts.
Ensure you have part number and reference designator on the individual part bags.
Manufacturing is just putting parts on boards, but it’s doing so with a whole lot of variables. A few extra checklist steps can go a long way toward removing variability of those variables.