Circuit Board Design and BOM Management in Low Volume PCB Assembly

Created: September 11, 2017
Updated: September 25, 2020

Birthday cake with candles

What’s the difference between Angry Birds and SpongeBob? I’m probably at an age where I shouldn’t be caring about these things, but choosing the wrong character for my son’s 5th birthday cake could spell disaster.

As a designer, you probably can’t relate to my need to carefully consider the repercussions of choosing SpongeBob. However, you might understand it better knowing that I apply the same level of caution when designing for low volume manufacturing. Even worse than ruining a child’s birthday party, a single mistake in low volume manufacturing can wipe out the product’s profit margin, along with the smile on my supervisor’s face.

How small decisions can drastically increase the cost of PCB production

When only a couple hundred of a specific PCB model is produced a year, each design iteration due to poor design decision can impact the profitability of the product. So does having to create an unnecessary stencil setup that increases the PCB assembly cost by 30%. It’s also important to consider the availability of each component you choose for your design. I once opted for a connector that was more popular at the time without considering its availability in my region. This resulted in a longer lead time, higher shipping costs and having to build up an excessive inventory on site to mitigate these factors. Here are some tips on how to avoid these situations. 

8 Important considerations for profitability in low volume manufacturing

1. Use Commonly Available Parts

Besides cost and functionality, the availability of a particular component is important when it comes to low volume production. Certain projects may require you to commercialize your design quickly, and waiting for months for a single component could jeopardize your entire project. Before you decided on a particular component, be sure to check that they are easily available from your local suppliers.

2. Avoid Components With Short Life Cycle 

In my early career as a design engineer, my supervisor wouldn’t allow us to use components that were also heavily used in automotive and mobile applications. This was because the mobile and automotive industries were evolving faster than our industry in terms of electronics and so these electrical components were more likely to have a short life cycle. As a result, we avoided having to revise our designs as often due to component obsolescence. 

3. Place All Surface Mounted Components On The Same Layer

The cost of stencils used in surface mounted components assembly is significant in low quantity manufacturing. Rather than trying to save costs by placing components on both the top and bottom layers of your PCB to minimize your board size, you can place all of the surface-mounted components on a single layer and save the cost of one stencil. Depending on your board, this can reduce your assembly costs by 25%.

PCB with mounted electronics
Having all SMD components on the same layer means you only need one stencil.

4. Panelize Your Design

Panelizing your design is a cost effective measure that can also shorten the lead time of the assembly process. Your supplier may charge a setup cost to panelize your PCB but the overall cost savings makes panelization a preferred option in manufacturing your PCB. 

5. Flying Probe Test

You can’t cut costs by skipping the post fabrication electrical test for your PCB. However, you can choose the best method of testing based on the nature of your project. If there is a high chance that your design will need to be revised in the future, choose the Flying Probe Test since it does not require a setup cost. 

6. Include Assembly Friendly Design Features

Omitting fiducial markers and dummy strips from your design can prove to be costly. Assembly machines need fiducial markers to precisely mount surface mounted components. Dummy strips are essential for leaving space for machines to clamp onto the PCB. Forgetting these important features could incur unnecessary post-assembly costs. 

7. Establish A Systematic Post Assembly Test Procedure

Having a lower volume of PCBs doesn’t make it any less important to quickly test and isolate defects. A properly constructed test procedure could save precious time in quality control and ensure a timely delivery. You don’t want to keep your client waiting while your team struggles to make sure that the PCBs are functional.

8. Prepare An Accurate BOM List

The last thing you would want when manufacturing a low volume of PCBs is to miss a crucial component and delay the assembly process. Omitting a component in your BOM list and having to resort to manually placing the part on your own is something that can be avoided. Trust me, you don’t want to have to solder one hundred connectors by hand because you forgot to add it to a spreadsheet. Bottom line, always ensure that your BOM list matches the sample that you are sending into your PCB assembly supplier. 

Manual assembly of PCB
Mess up on your list and you may end up with loads of manual rework.

The burden of making the right decisions to ensure a healthy profit margin for low volume PCBs is on us, the design engineers; however, it doesn’t need to feel like one. Altium’s BOM tools can make your life easier by automatically creating and updating your bill of materials inventory. That way no components are accidentally omitted and they can be monitored for obsolescence. 

Have a question about component management? Contact an expert at Altium.

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