How lesser-known printer software features can improve process control.

As a process engineer specializing in the stencil printing operation, I understand why many operators are unaware of the bells and whistles in advanced printing platform software – especially when working in a busy production environment. While the primary focus is speed, pressure and angle to ensure the best print at the fastest cycle time cadence, sometimes the production pace can be interrupted by unexpected events. I was reminded of this – and a couple of software tricks – recently when doing evaluation work in our lab.

A “rougher” foil may improve stencil performance.

A high-performing stencil printing process deposits the right amount of material volume in the right place, at the right time, and at the lowest cost per print achievable. Every assembly professional strives for this utopia, leaving no solder paste stuck in the apertures or smeared on the underside of the stencil. Naturally, with all the variables, this state is difficult to achieve 100% of the time. A perfect gasket (board to stencil) does not exist in the electronics manufacturing real world. Transfer efficiency is managed through aperture designs to provide the desired material volume on the pad, and solder paste smear (or its potential) is alleviated by cleaning the underside of the stencil between prints to avoid bridging. Cleaning, of course, comes at a cost – both in consumables use and in production time. If more high-quality prints can be achieved between necessary cleans, consumables overhead will be lower and throughput will be higher. 

The top eight fixes in the fishbone diagram to get back in spec.

The last column focused on making a “green light” stencil printing process more efficient, but for a not-so-green – maybe a bit more amber – print operation, some tried-and-true troubleshooting methodologies can get high-yield boards moving again. As I’ve noted before, myriad stencil printing inputs can affect outcomes. The famous fishbone diagram, noted in FIGURE 1, can seem daunting at first, but by taking a methodical approach to understanding the root cause of a problem, it’s relatively straightforward to get printing back in spec.

The time to squeeze out more efficiency is when everything is in spec.

What kind of approach do you generally take? Do you follow the “if it ain’t broke, don’t fix it” mantra, or are you more the “it’s good, but it could be better” type? In electronics manufacturing, continuous improvement is often discussed, but how much does your organization adhere to this philosophy when the shop floor is humming and everything is within spec? This is when process engineers should try to squeeze out even more efficiency.

Certainly, there is urgency around a process that is not running as it should. However, when all the lights on the line are green, there is likely opportunity for more improvement than you realize. Consider challenging the process through the lenses of incremental cost reduction and quality enhancement.

In the stencil printing process, there are several possible avenues for lowering cost and raising quality, even when everything is within spec:

Cost down. The first and most obvious area for resource optimization is understencil cleaning. This sub-process of stencil printing has several costs associated with its operation, including time (output reduction) and a fixed cost (fabric and solvent consumables) for every clean. A majority of print platform suppliers ship equipment with relatively liberal default settings for fabric advance (how much is used for each clean) and solvent volume. This is based on assumptions a manufacturer may be cleaning a very dirty stencil with numerous apertures across the entire length of the fabric, so high debris removal must be accommodated. In essence, the defaults are set for worst-case scenarios, as is fairly standard practice. Optimizing these settings based on specific process conditions has the potential to reduce waste through streamlined consumables delivery.