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First, we asked you to send in your questions for Happy Holden. Now, it’s Joe Fjelstad’s turn! Inventor, columnist, instructor, and founder of Verdant Electronics, Joe has been involved with rigid PCBs and flexible circuits for decades, and he’s ready to share some of his knowledge with our readers. We hope you enjoy “Just Ask Joe.”
Q: Will standardized grid designs ever come to fruition?
A: I am old enough to know that once upon a time, the electronics industry actually had a standardized grid. It was 0.100”. It was the natural by-product of the fact that most early electronic packages were dual in-line packages (DIPs), and nearly all of the first DIPs had their leads on 100-mil pitch (the Soviets and Eastern Bloc nations went with 2.5 mm rather than 2.54 mm or 0.1 inches). It was a natural default, and 100-mil grid pitch design was common and the standard even today; think of hobbyist’s bread boards, which are on a 100-mil grid.
Those halcyon days were disrupted as pin counts rose, and surface-mount technology took the stage to help manage the explosion in package pin counts. Then there was the “80% rule” for package leads that took effect to provide a defined roadmap for following generation component lead pitch. Thus, today (ignoring inch-based devices), we have 2.5 mm, 2.0 mm, 1.5 mm, 1.25 mm, 1.0 mm, 0.8 mm, 0.65 mm, 0.5 mm, 0.4 mm, etc.
Area array technology offered the opportunity to return to a standard grid, but the 80% rule was applied instead, which is a great pity from my perspective. Instead, what might have been done is to agree on a common base grid pitch and depopulate to the pin count desired. Everything gets easier again—no more burning off layers of circuits to accommodate escapes and differing grid pitch components. It is an easy way to return to standardized grids. All that is necessary is for component packagers to offer every component with terminations on a standard grid. My suggestion is 0.5 mm because that is where component soldering yields start to fall off.
Is it possible to return to the standard grid? Absolutely. It is more a question of customer demand for such and package foundries’ willingness to do so. It could save billions of dollars annually, according to my back-of-the-napkin calculations.
To pose your own question for Joe Fjelstad, click here.
Joe Fjelstad is founder and CEO of Verdant Electronics and an international authority and innovator in the field of electronic interconnection and packaging technologies with more than 185 patents issued or pending. To read past "Flexible Thinking" columns or contact Fjelstad, click here. Download your free copy of Fjelstad’s book Flexible Circuit Technology, 4th Edition, and watch the micro webinar series on flexible circuit technology.