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Getting to Know Your Designer
In this issue, we examine how fabs work with their design customers, educating them on the critical elements of fabrication needed to be successful, as well as the many tradeoffs involved. How well do you really know your customer? What makes for a closer, more synchronized working relationship?
In this issue, the biggest names in PCB manufacturing share their economic outlook for the upcoming year and beyond. As you will see, they were all bullish on our industry, but there was some apprehension as well. No one wants to get burned by another the supply chain disruption.
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Microvias Can Be Stacked in Certain Package DensitiesOctober 13, 2022 | I-Connect007 Editorial Team
Estimated reading time: 2 minutes
Summit Interconnect’s Gerry Partida recently spoke with the I-Connect007 Editorial Team about his research into root causes of weak microvias. Rather than a single manufacturing process cause, Gerry suggests that microvia reliability is the culmination of several material interactions and that contrary to popular belief, microvias can still be stacked in small, tight packaging densities. He highlights the need for simulation, as well as some of his findings that he plans to publish in a paper at IPC APEX EXPO 2023.
Nolan Johnson: Gerry, I understand your team has been doing some research into microvia stacking and will have a paper at the upcoming IPC APEX EXPO on this topic. What have you been learning?
Gerry Partida: Remember back in the early days of HDI, we would stack microvias as deep and plentiful as we wanted to? Then people started experiencing intermittent failures. Boards got hot, the components would fail, and it went back and forth. Manufacturing did something wrong, the assembler overbaked the boards, and it would go back and forth again. A lot of designs started to suffer, especially certain military products that would stack microvias. We would ask, “Why isn’t it working? Why does it work when it does work?” Most of the microvias that were stacked originally were small BGA packages. They were 0.4 mm or 0.5 mm, and those densities drove you to stack. These designs often were for the commercial OEMs, but if something failed, the commercial guys didn’t come back to discuss the issues.
But for the military guys who have ASICS that cost hundreds of thousands of dollars each, the stakes are much higher. If it is for space, then it can only be assembled once for flight; it cannot be taken off and reused. The military packaging then was a much wider pitch than the commercial guys who were stacking microvias initially.
When we looked at where the failures were happening, they were still happening with the commercial guys who were going three or four deep stacking microvias. They weren’t trying to make short, squatty, wide-diameter microvias because they were using thicker dielectrics to get wider lines for impedance. Consequently, we went for a time where there really didn’t seem to be a problem. Then it became, “We see a fracture at the target pad on the stack of the microvias,” and everybody thought there was a weakness in the electroless copper.
We all came up with these rules of thumb: Don’t stack more than two. A lot of DOEs were done, and they almost always concluded, “Do two stacks, then stagger off.” That seemed to work. Even fabricators we would work with had rules like, “Keep your aspect ratio for a single microvia at 0.75 to one. If you’re stacking them, keep them at 0.6 to one.” That seemed to work; we got good results.
Now, during this time we employed reflow resistance testing to monitor the strength of connections in the finished product. We started learning more about what works, and what doesn’t work. Some designs would slip through, where they do a three-stack on tight pitch, and they were passing. We were asking that if our rule of thumb was only two, then why is it working at three? When you look at the design, it’s a 0.4 mm pitch.
To read this entire conversation, which appeared in the September 2022 issue of PCB007 Magazine, click here.
After working for a capital equipment supplier for almost 50 years, I’ve found that the most important part of getting to know your vendor is good communication among all parties. While contact between fabricators of a constantly changing product line and the designers of those products may occur daily or weekly, conversations between you and your equipment supplier may be years apart. That lengthy gap often means that previous contacts may have been promoted, retired, or moved on to other opportunities. You may have also migrated to a new supplier with whom you have little or no history. In either case, you will be interacting with someone you are unfamiliar with (as they are with you). Therefore, it is essential for both sides to communicate clearly so expectations will align.
The opening session of the second day’s conference proceedings focused on global PCB trends and was introduced and moderated by Dr. Michele Stampanoni, vice president of strategic sales and business development at Cicor Group in Switzerland. He opened the session with Dr. Hayao Nakahara’s knowledgeable and enlightening video presentation on the IC substrates industry.
The 2024 Winter Conference of the EIPC took place January 30 and 31 at the IHK Academie in Villingen-Schwenningen, Germany. The keynote session will be reported separately. Here is my review of the first day’s conference proceedings.
Electrodeposition comes down to fundamentals. In the early days of plating, many users considered the nuances of metallization as black magic. Those days are long gone. Having a thorough understanding of the critical parameters that influence electrodeposition will determine success.
High Density Packaging User Group (HDP) is pleased to announce that Shikoku Chemicals Corporation (Shikoku) has become a member.