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The Bare (Board) Truth: How to Qualify Your Fabricator

This column appeared originally in the Inside Design Newsletter.

In today's column, I will be talking about what makes a good fabricator from the customers' viewpoint.

So, what it is you really want from your PCB fabricator? What should you expect?

• Quick responses to your RFQs? 
• Outstanding quality? 
• Consistent on-time delivery? 

Your answer should be "All of the above!"

So, let's start with the quote process. Ultimately, whether the job is a quickturn or standard lead time, you - the customer - would really like to see all quotes back within a couple of hours, not a couple of days.

Additionally, you want to see accurate quotes that take into account all additional processes. It's never good when, once quoted, the fabricator comes back with additional costs for unforeseen processes.

Again, this is why it is key to get a manufacturing review done if anything outside the norm is requested on the drawing or quote. These include points like the proper review of impedances to make sure materials are available and the impedances work without requiring large variances in either dielectric or line sizes, buy-offs for any deviations of material type or copper weights, etc.

Beyond the quote process, you want a fabricator that is CAPABLE of all required processes to ensure the part is built as expected. You want the company to be IPC Class 3 6012 capable and ISO-certified, and you may need them to be ITAR-certified as well.

Even if you cannot visit the shop for a physical qualification, send in a job to quote and watch the response. A good fabricator will be diligent and get back with you within a couple of hours, including a preliminary examination of the files, impedance calculations and proposed stack-up if impedance is dielectrically controlled. The company should also be able to let you know right away if the job does NOT meet their process minimums and cannot be built. If deviations are allowed, in many cases a good fabricator will also provide alternatives, such as a deviation for material type, starting copper weight, dielectrics or line sizes.

This communication line between the fabricator and the customer is crucial to understanding the customers' needs properly. Your fabricator's Sales/Quoting personnel should be prompt in their response, courteous and sympathetic to your needs. Sales people should have excellent prioritization and organizational skills to be able to accommodate standard and expedited lead time quotes all in a timely manner.

As far as the fabricator's quality is concerned, "the proof is in the pudding." If you are receiving multiple phone calls from a fabricator regarding remakes of your parts, you may want to seek a secondary source.

Quality goes well beyond "skin deep" with PCBs. Functionality of the part is key. A good fabricator does NOT play tricks with plating and mask thickness in an effort to achieve an impedance goal. During facility tours here, I always say that we would be doing you a disservice by disguising or compromising on the parts.

For example: Let's say we over-etch a surface and get higher-than-predicted impedance readings prior to solder mask. True, we could add an additional coat of mask material in an effort to bring the impedances within tolerance. But what if the job is ordered as a repeat and this time it is properly etched and does not require the additional coat of mask to keep the impedance in tolerance? You, the customer, now have two sets of boards. Both meet 50 ohms of impedance, but have slightly different electrical performance.

Not good, and not good business.

A good fabricator will use a goal-seeking tool, such as a Polar Instruments impedance calculator, when calculating impedance. This can determine up front what slight tweaks need to be done in CAM to stay in the middle of the tolerance, as well as literally calculate for things like over-etch and under-etch, too little or too much plating, and too little or too much mask material, based on the fabricator's known process minimums.

Recovery time is a big issue. If something SHOULD happen in the fabrication cycle that requires a remake, look for a shop that minimizes recovery time and has a process plan to minimize its chances of reoccurrence.

Likewise, if a fabricator is consistently late on orders, you may want to seek another fabricator. A good fabricator, especially in the fast-turn prototype environment, understands the customers' time-to-market constraints and meets the expected deadlines, even sometimes shipping early if the customer allows.

By the same token, if you know me, you know I am a big advocate of communication to minimize costly iterations. Not only does communication keep the revisions to a minimum, but in a proto environment, we can share with the customer possible concerns about transitioning to larger volumes.

I can't tell you how many times I have had customers thank me for that last one. Offshore volume shops may be low-cost, but the product must still perform as expected. Prototype shops have traditionally pulled off things production shops balk at in large volume.

Of course, cost is always a factor. But a smart board buyer also knows the value of quality, service and delivery can have a huge impact on the overall cost of the product's market cycle.

As always, I thank you for your time. Please feel free to contact me with any questions.

 Mark Thompson is in engineering support at Prototron Circuits. He can be reached at MarkT@Prototron.com.