Designing in a Vacuum Q&A: Mark Thompson


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I-Connect007 Columnist Mark Thompson of Out of the Box Manufacturing has been in CAM engineering for decades, and he’s also worked as a PCB designer, so we knew he would have a few things to say about working in a vacuum. As he explains, the designer isn’t the only stakeholder in the process who feels like he’s working inside the dust bag of a Hoover upright. 

Andy Shaughnessy: How often do you design a board without knowing who is going to fabricate and/or assemble it? 

Mark Thompson: That depends on the complexities of the given job. As an example, if the job/design has controlled impedances, a good design bureau or company will consult with the fabricator for the lines/spaces and dielectrics needed to achieve the impedances prior to design and layout. So, the designer knows who will be fabricating the job. If there are special considerations, the design engineer may even visit the facility to make sure they understand the intricacies of the job. Many companies will have a design engineer or a field application engineer pre-qualify a fabricator to make sure they can do the work and go over any details necessary to pave the way for success of the job.   

I have heard of designers “camping out” with the fabricator for the entire fab process if the board is extremely involved. Additionally, it helps for designers and fab engineers to have a solid working relationship. If the designer and fab engineer are working together for the first time, when the fab engineer has a question about the design, he will typically call the contact person (often a project manager or purchasing person), who will connect him with the designer. This is where a great fab engineer who asks unpleasant questions is indispensable.  

Unfortunately, things may change, and the designer may not know who will be fabricating the part or even assembling it. For instance, the chosen fabricator may have a long lead time or some other previously unforeseen complication. In this case, the part may have to go with another fabricator. Please note: When this happens, if the job is controlled impedance, it is a good idea to have the new fabricator run the calculations to see if there will be any large trace or space swings that result in a redesign. This includes things like increasing traces when you’ve already designed to the minimum space allowance.  

Other hurdles, such as choosing a different material type (due to supply chain issues), may result in a complete redesign, which, unless you are a glutton for punishment, is not so fun. Likewise, the designer may have an idea who will be assembling it, and he may not. This is where I get on my soapbox. If you genuinely want to make sure something gets done, communicate it clearly. 

Shaughnessy: Why do so many designers not know who is going to manufacture their boards?  

Thompson: I can think of two reasons. The first reason is company culture. If the designer works for a company that has a purchasing department that does not share information about where the part will be fabricated, designers must ask probing questions. Companies today have numerous design and engineering meetings where this information can be shared, but frequently it is not, for whatever reason. I see no reason a purchasing person would intentionally withhold information regarding the selected fabricator, but it could happen.  

Remember that if cost is their sole reason to choose a fabricator, you get what you pay for. If a job requires multiple respins due to a fabricator’s lack of quality control, you have lost more than just time. I think that a thorough company will always share such information with the designer and engineer on that project, especially if there are any specific items to be passed along to the fabricator relating to the success of the part.

To read this entire conversation, which appeared in the May 2022 issue of Design007 Magazine, click here.

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