Penny-pinching Placements
A few cost-saving tips from a PC Board Assembler
The product development life-cycle usually begins with a set of requirements. Along with functional requirements there are cost requirements: your product must deliver superior functionality and cost less than the competitor’s.
The top-line dollar figure is the Cost of Goods Sold which breaks down into labor, materials and overhead. For Printed Circuit Board (PCB) Assemblies, these costs can be heavily influenced by the designer.
An Electronics Manufacturing Service provider is the fancy term for a company that takes all your electronic components and puts them on your PC Board for you. These are also called Contract Manufacturers. Let‘s simplify and call them Assemblers. The main tool in the Assemblers’ arsenal is the Pick and Place machine. These machines are what make mass-production of Printed Circuit Board Assemblies economical.
Let’s look at some tips on how to minimize the cost of PCB Assemblies:
Tip #1: Minimize use of through-hole components
Pick and place machines are optimized for surface mount components. Even at the largest assembler, insertion of through-hole components is almost always a manual labor task. Unlike machine-placed parts, any manual labor task adds an additional per-board cost which will not change appreciably with your order size. Therefore, reducing the number through-hole components will reduce your PCBA cost overall. When you are specifying connectors, for example, see if there are surface-mount versions. Oftentimes there are.
The only possible reason you might choose through-hole is for mechanical strength. USB connectors take a lot of abuse, for instance. This was the case for the 2016 Superconference Badge. A through-hole USB connector was chosen because of bad experiences during the prototyping phase. It ended up being ‘sort-of’ machine placeable.
Tip #2: Avoid Double-sided Assembly
There may be times when your physical size requirements demand that you put components on both sides of the board. Printed circuit board fabricators charge by surface area which may also tempt you. The simple truth is that double-sided assembly costs more. Let’s look at why. Here are the process steps for a single-sided assembly:
We apply solder paste to the PCBs, Run them through the Pick and Place machine, then through the reflow oven. The finished PCBAs are inspected and we are done. This glosses over the intricacies but that’s it in a nutshell.
Now let’s look at double-sided assembly:
The process is basically repeated twice. The first side is completed and then the board is sent through the paste, place and reflow steps inverted. It’s fairly obvious that this will add a good bit of assembly cost. There are also other complications if you have heavy parts like power inductors on both sides of the board. These parts will need to be a dot of glue applied to them so they won’t fall off when inverted during reflow. This will add another manufacturing step and more cost.
Tip #3: Reduce Bill of Materials (BOM) size
Your Bill of Materials (BOM) size is the number of unique Manufacturer Part Numbers (MPNs). Each MPN must be qualified and sourced, inventory managed, mounted and vision-trained on the Pick and Place. Now there are certain designs like RF boards where inductor and capacitor values are precise and cannot be altered. For the vast majority of designs however, things like decoupling capacitors, pull-up and pull-down resistors and LED series resistors are targets for BOM size reduction.
Summary
These are just a few suggestions. Applying any one of these tips may only result in a few cents of savings. Apply as many as possible and it could have a big effect on your Cost of Goods Sold.
Here’s a starter PCB Assembly cost-reduction checklist:
- Are there surface-mount versions of my through-hole parts ?
- Do I really need double-sided assembly ?
- Can I reduce the number of values used for decoupling capacitors ?
- Can all my pull-up / pull-down resistors be of the same value ?
- Do I really need a red, green and blue LED when 3 blues would do ?
- Can I replace those zero-ohm resistors with solderable jumpers ?
These are just a few suggestions. What are some others ?
