Circuits Assembly Online Magazine - Features

Features Articles

Mike Buetow Last month, a California jury awarded a resident $289 million, finding he had developed cancer from exposure to a popular brand of herbicide.

What, you may ask, does a guy who used Roundup to kill weeds around school buildings in the San Francisco Bay area have to do with me in the printed circuit board industry?

A lot, potentially.

I had the pleasure in August of interviewing Brenda Baney for our PCB Chat podcast. As some readers may remember, Baney previously was a regular in these pages. She was an excellent columnist: knowledgeable, opinionated and articulate. After two decades at Delco, she now runs B Cubed Consulting, where she provides expert guidance on conflict minerals, RoHS and REACH product stewardship, and the International Material Data System.

John Sheehan There are times increasing inventories and AVLs makes sense.

A constrained supply chain represents a challenge to Lean manufacturing processes, but in the electronics manufacturing services (EMS) market, the bigger challenge is often OEM misperceptions about strategies to address this. From a Lean perspective, navigating a constrained supply chain often requires taking one step back to move two steps forward.

Our November 2017 column discussed several areas where the best strategy was “at odds” with Lean manufacturing principles, including:

Plan further out;
Hard orders beat forecasts;
Increase the number of suppliers; and
The marketplace dictates it is smarter to carry more inventory.

Akber Roy Microvias have a domino effect, increasing available copper and lowering resistance.

Today electronic devices typically use designs with complex requirements that only high-density interconnect (HDI) technology can meet. Component manufacturers support the move by making components with smaller pitches. Because they are using more I/O connections, larger FPGAs and ASICs operate at higher frequencies, and the sharper rise times require smaller PCB features. The HDI PCB process supports these requirements exceptionally.

HDI PCB designs use microvias that offer a number of electrical benefits, and they also improve the power integrity of the assembly. This enhanced integrity comes from such sources and enhancements as decoupling capacitors, presenting a smaller mounted inductance, and chip pinouts requiring fewer perforations, thus delivering better performance from planes. The HDI PCB process also uses dielectrics of different thicknesses that reduce plane capacitance compared to conventional design.

Martin Wickham Too much heat during reflow can force solder out of a BTC.

FIGURE 1 shows examples of solder beads after reflowing bottom termination components (BTC). The beads are related to placement force prior to reflow, where the solder paste deposit is displaced away from the pads before reflow soldering. It is uncommon, but solder beads have also been seen coming from the package itself due to excessive heat during reflow. Solder beads or balls on the side of packages and close to the board surface are related to paste printing, paste volume, stencil design, PCB pad size, placement force or reflow, and can easily be demonstrated.

David Bernard The target style of the x-ray tube impacts magnification, resolution and quantity.

In last month’s column I explained the impact a transmissive or reflective target style of x-ray tube will have on the available magnification of an x-ray system. The difference between the two target types is shown in FIGURE 1. Not just the magnification is altered by the choice of target, however. The focus, or resolution, of the tube, as well as the flux, or quantity of x-rays, that the tube produces will also be affected. This is caused by the x-ray tube settings.

Clive Ashmore When diagnosing print problems, don’t overlook substrate support.

Substrate support is an important, yet often overlooked, element of the screen printing process. Sure, tooling is top of mind when all necessary parts of a new PCB assembly are being developed. But once it’s in the printer way down in the print nest on the table, we tend to forget about the tooling block. I suppose this out-of-sight, out-of-mind mentality is why manufacturers often point to more obvious, visible components of the printing operation as the culprit when the process shows inconsistency. Surely it must be an issue with the squeegee, the stencil or the board fabrication, right? Well, sometimes that’s the case. In many instances, however, a resolution may be as simple as a look at your tooling; something could have changed, or maybe it’s been incorrect from the start.

If the tooling isn’t manufactured properly or has been altered during production, printing inconsistency is the result – either across the board or from board to board. Paste volumes may be noticeably different in various areas of the PCB or panel; one corner may be just fine, and another has too much or too little material. This dynamic could be the first clue tooling is the cause. If the problem were an improperly manufactured stencil, for example, the issues would more likely be consistent across the entire board. Tooling errors can be extremely focused.