Tipping Points in Electronics Assembly

Manufacturing processes are complex beasts. Printed Circuit Board Assembly (PCBA) manufacturing is no different. Your Bill of Materials (BOM) only represents the ingredients. There must be an assembly recipe. Like cooking, surprising things may happen when you try to scale.

A continuous Printed Circuit Board (PCBA) Assembly Line (image credit)

You may have wondered what factors affect PCBA costs as you scale. Why are prototype and pilot runs so expensive per-article? Why does the price per article plummet? When does it level off? There are these “tipping points”?
Industrial robots such as Pick and Place (P&P) machines do most of the placement work, so why are the costs still high?

Labor Factors

There is still plenty of human labor involved even at the largest Contract Manufacturer (CM). And it remains the largest part of operating cost. It is this cost plus margin plus overhead which makes up the per-article price.

The labor tasks in PCBA manufacturing can be put into two categories — Setup and Production. Setup tasks include parts check-in, loading parts onto feeders, and P&P Programming. Production tasks include: loading and unloading boards between machines, reloading parts, and correcting the occasional feeder jam.

Setup tasks can take many hours or even days of labor. At very low volume, it is not unusual for the setup of the job to take much longer than the production. At ultra-low volumes, it may be more cost-effective to do assembly by hand. This is actually the first tipping point but rarely seen outside of prototyping runs. Through-hole parts will still need to be positioned on the board by hand at all volumes. Larger CMs will have Selective Solder machines to perform the soldering step.

Reducing the number of through-hole parts to a minimum is essential to reduce PCBA cost.

This is a core tenet Design for Manufacture (DfM) to keep in mind during the product development phase.

Printed Circuit Board Assembly Time at Low-volume (image credit)

As production time increases setup time remains generally fixed. So, setup time represents a smaller and smaller percentage of total time. This is why you will see the per-article costs drop. Setup time is being amortized over production time.

Printed Circuit Board Assembly at High Volume (image credit)

Of course, costs do not drop to zero. They level off. This is the another tipping point: where the per-article cost is only a factor of production costs. At this point, the CM is boxed in by their level of automation. If your job is on a large continuous line (all machines connected by conveyor) then your per-article costs will be lowest. The drawback is that these automated lines take longer to setup. The volume must justify it. Runs greater than 1000 articles are the norm. The planning and quality assurance processes also become much more rigorous. Scrap rates must be reduced to the single digit percentages. As your production size grows it may be that you will be forced to transition from a low-volume CM to a high-volume one. Or, you may need to go from an on-shore CM to an off-shore CM. It is very important for your enterprise to capture and document as much of the knowledge gained from these relationships in-house. This will smooth the transitions.

Finding your tipping point

Ultimately you will need to work with your CM directly to figure out how to reduce costs and setup time. The DfM process is an iterative exercise, but talking to them up front will help you understand the steps that will save you the most money and have the highest chance of success for your PCB assembly.

How have you managed to reduce assembly costs in your designs? Let us know below.