Proper fab specs can prevent a deluge of engineering questions.
I have been selling bare printed circuit boards for over 30 years to a variety of customers who order a wide selection of PCBs. The most common complaint I hear from board buyers is about the number of engineering questions (EQs) asked whenever a new order is placed, or when a part number is moved from one supplier to another.
"Why can't you build the boards without all these questions?" they ask. "We sent you the working files!"
To many buyers, the inevitable EQs that come along with moving a PCB order to a more cost-effective supplier seem daunting. Sure, the new pricing may be great, but many PCB buyers will delay switching to a new supplier because they don't want to deal with engineering questions from the new fabricator.
I hate EQs just as much as the next sales guy. Who wants to bring up a problem or concern to possibly scare a customer or delay an order over what might seem a minor issue? But it is business malpractice when buyers are knowingly leaving money on the table because they don't have the time or knowledge to properly order PCBs from better suppliers just because of potential EQs.
And sometimes it's not just wasted money; the quality performance of the incumbent vendor is permitted to slide, again because buyers are hesitant about facing those pesky questions from a new vendor.
Purchasing and engineering personnel need training to be able to properly relay all the information required to properly build a PCB.
Some board buyers would rather a PCB vendor make assumptions about an order and not bother the customer with questions about changes or modifications. Could a PCB vendor make a buyer's life easier this way? Sure. But should they?
How much leeway or license should a buyer grant to a vendor to make assumptive changes to the customer-supplied artwork? I understand the delivery clock is ticking and the customer wants the order as soon as possible. But who wants to populate boards with expensive components only to have them fail at the end of the assembly line?
PCB vendors want to build orders correctly. Their questions help protect their interests and those of their customers. It's worth it to take the time to answer all questions completely.
Here are some tips for buyers on how to minimize EQs after the order is placed to help speed orders through the manufacturing process:
- Although not all buyers have the expertise to do this, files need to be checked before being sent to fabricators to ensure orders have all required information and that they fall within industry (and possibly company) manufacturing standards.
- Many old fabrication drawings need to be updated. Often, companies lack a documented PCB fabrication specification that manufacturers can reference when they receive information that is incomplete or needs clarifying.
- If documentation is lacking, nothing beats an actual sample of the PCB that was built before. Plenty of information can be gleaned just by looking at the actual board. And yes, an emailed photo(s) works wonders too!
- "Print states: Build to IPC Class 2. Is that IPC-A-600 or IPC-6012?" This simple question means a world of difference when it comes to the amount of testing and paperwork required – which means a much higher price. The customer might require all that additional paperwork to confirm the assembly meets its needs. If the proper paperwork isn't with the boards at delivery, the assembled product might be useless. Be sure to answer this question. By the way, "Just build commercial" is not an acceptable answer, as both IPC-600 and IPC-6012 are commercial specifications.
- "Are X-outs allowed?" To save on PCB costs, some assembly operations can accommodate PCBs that are provided in array or panel format with X-outs – nonfunctional boards – while other assemblers cannot or will not accept X-outs. A corporate PCB fabrication specification spelling out customer preferences addresses this issue and saves time.
Surprisingly, many companies, including some well-known OEMs and plenty of EMS firms, do not have a corporate PCB fabrication specification that is unique to their operation or assembly needs.
This document can be as concise as a few pages. It should outline everything from acceptable material types to desired metal finishes to final packaging and storage requirements. It should also include panelization instructions.
Corporate fabrication specs should answer most EQs. You might get specific queries about dealing with artwork tolerances, for example, or the need for a stackup variance to permit controlled impedance. Those questions would have to be answered individually.
Companies can save a great deal of time and get fewer questions by creating fab specs and then ensuring they are fully understood within the firm and among the vendor's engineering personnel.
The bottom line is PCB buyers should be thankful for engineering questions. There is a direct correlation between the number of questions asked and the quality of product received, and those questions will save your company money (and many headaches) in the long run. •
Greg Papandrew has more than 25 years' experience selling PCBs directly for various fabricators and as founder of a leading distributor. He is cofounder of DirectPCB and can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it..
