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36 SMT007 MAGAZINE I FEBRUARY 2020 When it comes to making consumers happy and electronic assemblers miserable, nothing achieves both quite like miniaturization. With our ever-increasing demands to house a full- size movie theatre with surround sound and limitless digital storage in the palm of our hands, the only way for CMs to respond is with miniaturization (and curs- ing—lots of cursing). In this installment, I'll revisit the history of shrinking packag- ing and lessons learned. The move to make prod- ucts smaller isn't any- thing new, but, at this point, it is a matter of scale. Making a computer's physical foot- print fit inside a room smaller than the size of a football field was a big leap, but a lot of the tech- nology required to do that didn't exist until that happened. There was a healthy amount of new component tech- nology being introduced into the industry at the time that made that process much easier in comparison to what the industry is work- ing with today. When the size of a prod- uct has already been reduced to the small- est thing you've ever seen, making that even smaller will require shrinking of every com- ponent that is already being used. Any time you reduce the spacing between leads or contacts with bias differential, you increase the risk of electrical leakage and elec- trochemical migration. Using parts with tighter spacing, or lower standoff will most likely require multiple rounds of verification testing to ensure proper processing of the flux activa- tors. As mentioned in previous columns, the product's end-use environment plays a very large role in reliability. This puts the focus on cleanliness after the assembly process. When the lead pitch is reduced, lower levels of conductive residue are required to create electri- cal leakage paths. When discussing the end-use envi- ronment, the main param- eter we look a t i s ava i l - a b l e a t m o - spheric moisture. The leakage fire trian- gle requires conductive resi- dues, atmospheric moisture, and electrical bias. Of those three ingredients, the one that is easiest to control is the residues. The reduction in component pitch puts a pre- mium on cleanliness to reduce the risk of den- Big Trouble Comes in Tiny Packages Quest for Reliability Feature Column by Eric Camden, FORESITE INC.

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