Transforming Material Exchange

Another changeover task gets an Industry 4.0 makeover.

“Work smarter, not harder” is a phrase that – perhaps surprisingly to some – originated in the 1930s. For nearly a century, this well-known mantra has challenged workers to manage tasks with intelligence and available resources to deliver more effective results. Today, we have significant technological advances and software capability to thank for helping analyze and automate processes for maximum efficiency. For the stencil printing operation, one of the most output-limiting tasks is product or stencil changeover. Changeover is necessary, but there is still room for efficiency improvement to minimize downtime.

It’s true that for many stencil printing changeover activities, engineering solutions have already been developed. There are more mechanically complex remedies, such as universal automatic board support tooling innovations, which have significantly reduced downtime. Software-controlled mechanics have also transformed procedures like stencil loading into the correct position, automatic rail width adjustments, alignment routines, and many other previously manual tasks. One action that hasn’t been successfully tackled, however, is material exchange. So, our company decided to take it on.

Solder paste preservation during changeover. Generally, there are three types of printing changeovers: full product, scheduled stencil interchange and error correction. The first occurs when a completely new product (including a different stencil) is put into rotation. The second may be less well known. In some high-volume manufacturing operations, as part of a preventative approach, stencils for the same product may be changed out every four hours, on average, even if the SPI indicates an in-control process. It’s just standard protocol. Finally, changeover may be indicated if errors are appearing in SPI. In all cases, solder paste material must first be removed from the stencil on the printer, set aside, and then put onto the newly loaded stencil. The only exception is if a total product changeover requires a different solder paste material (which is uncommon but does happen).

If you’ve ever managed a stencil printing operation and had to remove paste from the stencil prior to a changeover, you know that solder paste can be challenging to corral; it likes to migrate.  Getting the remaining paste off a stencil is a bit like trying to scrape jelly off a plate in an orderly fashion. It is and always has been an essential part of the stencil printing changeover routine, however. And an entirely manual task.

To further improve product and stencil changeover and move toward operator-free, Industry 4.0 methodologies, a new solder paste transfer concept has been developed. With this option and the push of a button in the operating software, solder paste is mechanically moved off the current stencil and positioned for reintroduction once the new stencil is loaded.

Here’s how it works: The printer’s squeegee pushes the material off the stencil into a customized tray that is attached to the print carriage. The tray is then moved to the back of the stencil printing machine and out of the way of the print nest. The transfer tray is held there until all other changeover elements are completed. Once the new stencil is loaded and production is ready to begin again, the other squeegee drives the material off the tray and onto the stencil into the correct position. If a new product has been introduced during changeover (and it’s not just a like-for-like stencil exchange) and the solder paste needs to be in a different position, the system knows where to deposit it. Then, the tray returns to its home position until the next changeover. The stainless-steel tray is detachable and easily removed for cleaning, if necessary.

This novel solution replaces the manual clearing of solder paste, eliminating the operator time associated with the task, and more thoroughly captures and preserves material until production resumes. Working smarter, indeed!

Caveat: As mentioned, some complete product changeovers require different solder paste materials. If this is the case, and a new solder brand or type (moving to Type 5 from Type 4, for example) is required as part of the changeover, the system wouldn’t be helpful for that product mix.

Clive Ashmore is global applied process engineering manager at ASMPT (asmpt.com); clive.ashmore@asmpt.com. His column appears bimonthly.