Achieving printing nirvana is largely dependent on solder paste material, print speed and deposit release.

Ahhhhh … screen printing utopia. We process engineers strive for this existence. In a perfect process, printed solder paste would emerge from the stencil as exact replicas of the aperture shape: nice, flat, brick-like deposits. And, while modern printers and advanced materials get us close, solder paste is still, well, solder paste. The materials are not inks; they have a grain structure that is getting smaller in size and distribution and is suspended in flux. Try as we might, with these particles, there will be material undulation at best, and flat paste surfaces will likely never be a certainty.

With printing, we must be pragmatic. It’s not a digital process, and many variables come into play. The goal, of course, is to fill all the apertures on the stencil fully with solder paste to obtain the best deposit shape and volume possible. This is easier said than done, as the range of aperture sizes across a stencil can be broad, with 1mm square, 300µm and 200µm openings next to one another. Each of those apertures – from the very large to the very small – must be filled. Since printing with different thickness stencils is a nonstarter (generally and practically speaking), compromise is required, and that challenges our utopian ideal. Squeegee pressure, stencil thickness, print speed and separation speed must be balanced to accommodate variations in required deposit sizes. When all inputs aren’t optimized and in perfect balance, solder deposit shape differences can have the potential to introduce process problems. Known in the printing world as “dog ears” on square or rectangular deposits and “witch hats” on circular deposits (FIGURE 1), these solder paste deposit peaks may be defect bugbears, especially in the world of high-density, miniaturized assemblies.

When I first started in electronics back in 1991, through-hole was still dominant and SMT was just taking hold. It wasn’t long after, however, when we began hearing about multichip modules, or MCMs. Conferences sprung up, publishers dedicated entire issues to the subject, and trade groups started writing standards.

And then … not much. MCMs never became the dominant packaging style some analysts predicted.

But will they?

When the Semiconductor Industry Association ceased its roadmapping activities, a host of organizations, including IEEE, SEMI, ASME and others, jumped in. Last month, they launched the second edition of the Heterogeneous Integration Roadmap. Heterogeneous integration refers to the integration of separately manufactured components into a higher-level assembly (SiP) that, in the aggregate, provides enhanced functionality and improved operating characteristics.

From additive manufacturing to autonomous vehicles, figuring out the next big thing is no small chore.

With the last quarter underway and all eyes beginning to contemplate what and how to do better in the year to come, one of my focuses is trying to identify which technology will be the next big thing – one that will either transform or disrupt doing business as I know it.

Over the past couple years politics seems to have been the biggest disrupter for all types of businesses. As challenging as it may be to identify the next tariff or tweet that may or may not send markets – and customers appetite to buy products – into a tailspin, the real challenge is trying to identify the next technological breakthrough that will either propel my business and the greater electronics industry forward or retard them into oblivion. Over the past dozen years many technological initiatives have been touted as game-changers; however, to date none has truly had the big bang effect on our industry.

Talk isn’t cheap, but the absence of it could cost you even more.

Throughout my PCB career as a go-between for board buyers and manufacturers, I’ve often heard complaints from buyers that fabricators – domestic and offshore – ask too many engineering questions (EQs) after receiving an order. “Why can’t they just build the board?” buyers say.

This mystifies me. In my view, PCB vendor questions provide valuable feedback. They may indicate the vendor lacks all the required information to build the order. They also tell me the manufacturer is intent on gathering all the data necessary to do the job right.

I’d be more concerned if no EQs came from a vendor. A PCB has over 100 separate required manufacturing processes, almost all of which are unique to each customer. It would be surprising, even alarming, if everything in an order was absolutely clear, with no back-and-forth necessary.