Reading time ( words)
We asked for you to send in your questions for Happy Holden, and you took us up on it! We loved them so much, and we know that you did too, so we’ve compiled all 21 questions and answers into one document for easy reference.
Calculating Trace Temps in a Vacuum
Q: For space applications (without air), how should we calculate external layer current-carrying traces against the IPC-2221 (formerly IPC-D-275) charts?
A: I have never studied that, so I turned this question over to an expert, my friend Mike Jouppi, former committee chair of IPC-2152 Standard for Determining Current Carrying Capacity in Printed Board Design. This standard will provide many answers to your questions. Mike wrote Chapters 22 and 23 in the seventh edition of the Printed Circuits Handbook, edited by Clyde F. Coombs and me.
Mike answered: I'm a mechanical engineer who worked as a career thermal analyst. The charts in IPC-2152 in almost all cases will be conservative (both air and vacuum environments). The vacuum is for space environments. The purpose behind these charts is misconstrued by most users. My intention when they were developed was to use these charts as a baseline for developing thermal models that could be used to better understand the actual temperature rise of conductors in actual designs, which I did for my own design purposes. The concept did not catch on.
There is a significant difference between the temperature rise in a conductor, tested per IPC-TM-126.96.36.199a, and most PWB design configurations. The reason is that most designs have copper ground and power planes that conduct energy away from the traces. In addition, most designs in space applications have a significant conduction path from the PWB through-bolted fasteners or wedge locks to a sink.
Since the question does not include IPC-2152, I would recommend researching IPC-2152 and accounting for the power dissipations in the traces in the thermal design. I also recommend accounting for the conductor power dissipation in all designs, especially if the designers are not familiar with sizing parallel conductors. Parallel conductors are easily managed with accounting for conductor losses (power dissipation). FYI: It was the power dissipation in conductors that motivated me to lead the development of IPC-2152.
Ranking the Top Countries by Fab Technology and Production
Q: In terms of overall PCB fabrication capability, how would you rank these countries in terms of technology and production, today and in 10 years: USA, Japan, Korea, Taiwan, China, Thailand, Vietnam, India, Germany, and the U.K.?
A: I don’t have a crystal ball, but here is my best guess:
Manufacturing Issues From a Designer’s Viewpoint
Q: What do you think are the biggest PCB fabrication/assembly issues from a designer’s perspective?
A: Communication and education! Designers need to know a lot about electrical circuits and their performance, but equally important is knowing how that circuit will be manufactured. But manufacturing is usually not part of a designer’s education, so designers have to go out of their way to meet the manufacturing community and to communicate with them on issues related to their designs. IPC and SMTA make this type of training available, but a designer has to be aggressive in learning about manufacturing and all the do’s and don’ts.
Flexible Circuit Technology of the Future
Q: What do you think will be the next leading-edge technology for flexible circuits?
A: Disposable and wearable substrates, including paper
Monitoring Via Reliability on a Lot-by-Lot Basis
Q: What is the best way to monitor microvia reliability on a lot-by-lot basis for high-volume production?
A: What I recommend, and practice, is this: Do a thorough qualification of a fabricator using a HATS Qualification Panel (an IPC PCQRR-like panel) that includes an IPC D coupon resized for the runner on your SMT panel. Run these panel coupons through IPC-TM-650-2.6.27B and then TM-650-188.8.131.52 thermal cycles for 500 cycles. This is your baseline.
Then, by incorporating this smaller D coupon on all your boards’ assembly runners—requiring each lot to have a plating process control coupon for X number of solder float tests at 288°C and then microsections to look at TH quality—you have a way of comparing that lot’s performance to your initial qualification for that vendor. This should be redone each year and kept for records on each lot in case needed later.
The Future of 3D Printing
Q: What is your opinion on the 3D printers that can utilize both conductive and non-conductive inks? Is this the future of PCBs?
A: These 3D printers are evolving rapidly. A must is that the printer has the ability to use a number of different inks for the different components of a PCB, including the curing of the inks. At a minimum, that is:
- Insulating substrate
- Low-ohmic conductive ink
- Non-conductive insulating crossover
As the equipment improves, solder masks, resistive/capacitive and solder paste inks, and even semiconductor inks would be nice. Currently, this is a quick-turn application for a few breadboards.
Whether this technology moves into being a source of operational electronics with sufficient reliability will depend on the innovations in creating future inks. Conventional PCB production continues to innovate to reduce their turnaround times and costs, forcing 3D printing to work that much harder on their solutions.
What Would You Change About the Industry?
Q: If you could change/improve one aspect of this industry, what would it be, and why?
A: TQM/continuous improvement (or Six Sigma) is a philosophy that has stuck with me since I was first exposed to it. I even taught the engineering aspects of TQM to every one of my engineers and techs; this included engineering statistics from the free NIST Engineering Statistics Handbook, as well as enhanced problem solving. Then, I would have my engineers teach TQM to their production supervisors, foremen, and leads, who would—with the help of the engineers and techs—teach it to all of the workers.
Continuous improvement is a strategy for success. And in our challenging industry characterized by innovation and change, continuous improvement and customer satisfaction are the only ways to survive and prosper.
Is PCB Fab Returning to the U.S.?
Q: If the U.S. brings more PCB fabrication back to America, will it more likely be to the captive or contract shops?
A: There are only a few captive fabricators in the U.S., but I hope that more OEMs will consider going captive as a way to ensure a source of supplies, lower costs, minimum lead times, and continuous improvements. OEMs should emulate the activities of Whelen Engineering, the emergency lighting company in New Hampshire that went captive and returned all of its PCB fabrication from China. Whelen cut its costs in half, improved quality, ensured its IP security, and cut weeks off their cycle time—all with an investment that had an ROI of fewer than two years.
But if PCB fabrication is to return to the U.S. from abroad, the majority will be to contract shops. If so, I hope that the OEMs will consider partnering with those contract shops and not treating their manufacturing “as just another commodity,” just as they don’t consider their proprietary circuits to be commodities. How circuits are manufactured is not like making soap; each PCB is different and deserves the necessary focus and care in its construction.
Electroless Copper vs. Direct Metallization
Q: What are your thoughts on electroless copper vs. direct metallization?
A: Both get the job done! Electroless copper is the more traditional method but may have some problems with its internal crystalline strength when used with stacked microvias. Direct metallization is a newer technology that has come a long way in their development and is one of the few ways to successfully metallize polyimide film for flex.