Why standardization only goes so far.

Take a little trip with me to PCB Wonderland. PCB Wonderland is where all parts fit on the board; all component footprints and land patterns are perfect, and the design is finished on two fewer layers than the budget called for. In PCB Wonderland the design data are spot-on and exactly what the fabricator needs to get 100% yields. The bare boards are completely in spec and delivered a day early. At the assembly house all the parts are in stock by the time the boards arrive and, again, the yield is 100%. All the finished assemblies pass test and are delivered early.  In PCB Wonderland the design team gets a nice big bonus and a week off with pay for a job well done.  

WAKE UP!

Sorry to do that to you, but the little trip down the rabbit hole is what happened when I dozed off in the middle of Alice In Wonderland a couple nights ago. I finally realized it was just a dream when the guy who delivered the product turned out to be Johnny Depp in a top hat.

I’ve heard (or read somewhere) that our dreams are usually influenced by something going on in our lives. It may be a problem without an immediately obvious answer (I remember actually solving a routing problem in a dream) or something that is stuck in a region of the brain dealing with the subconscious. In this case, it may have been that I had been thinking about component tombstoning. After reading an online post about causes of components not doing what we intend them to do – in this case, settling their little selves onto the assigned pads and staying there – I’d been doing some research on the subject. I will admit that my research was not at the level of a doctoral thesis, but after reading several articles and talking to some experts in the field, I’ve come to the conclusion that there are more causes for the problem than there are words in this column (regarding the latter, about 750).

First, I asked whether tombstoning is as much a problem as I suspected. The overwhelming answer: a resounding “YES.”

Next, I asked the age-old query of every 5-year-old: “Why?” The first response was another question: “How much time do you have?” The causes piled up like Lindsey Lohan’s police reports. Even with the development of excellent calculators and industry brain trust specifications, land patterns are still a problem. While there may or may not be issues with the calculators or specifications themselves, there are other unforeseen variables. Take the component package itself. While component manufacturers standardize on package sizes and outlines through Jedec and similar organizations, one manufacturer’s “standard” package may in fact differ from what is presented by another manufacturer as the same component package, or it may be a case that the parts are counterfeit or otherwise not to specification.

Sometimes it’s a process issue. Every contract manufacturer has subtle or not-so-subtle differences in their processes (just like every designer, fabricator and EDA tool has different processes). One interesting suggestion was that if the paste were left unrefrigerated too long, it could make a difference in how it prints and reflows, and thus, the part could tip. I would never have thought of that.

In the end, I have to recognize that the goal of perfection in this context is laudable, but probably impossible to achieve. There are just too many variables involved and too many processes from start to finish. But we can focus on our area of execution, educate ourselves as best we can (for example, at PCB West in September; pcbwest.com), and get involved in all of the process to the maximum extent possible. Designers still are accused of throwing stuff over the wall. It happens before the design is done, and it happens after the design is done. While I’d like to take the designer’s side of every argument, I can’t always do that. I hear it too often from too many sources for it to be nothing more than a convenient excuse.

I suppose it is too much of a stretch to think that component manufacturers, design and manufacturing can come together to develop real standards, versus “recommendations”– the kind of standards that everyone in the supply chain would adhere to and that could help ensure everything would go smoothly. But I suspect those only exist in PCB Wonderland.

Stay in touch.

Pete Waddell is design technical editor of PCD&F; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .