Tips & Tricks: Generating Stencil Tooling


Reading time ( words)

Many engineers are leaving the editing up to the stencil fabricator these days, describing the PCB array, aperture undersize/oversize, shape conversions, etc., for the fabricator to then edit. From the outside, this may appear as a time saver for all of us overworked process engineers, but considering how many stencil redos have been required and how many processes that have run “sort of OK,” there’s a tremendous amount of scrap and rework that could be saved from just a little more attention paid to stencil tooling. I prefer to make my own mistakes rather that receiving a stencil (with the project due tomorrow) and finding that someone else didn’t do something right, or misunderstood my design intent.

It’s a huge advantage for the experienced engineer to be able to produce good, first run results most, if not all, of the time. You can learn what works best for your equipment in your environment. There are several Gerber editing tools available that will let you create a library and apply changes semiautomatically or automatically to your data.

One of the most common edits used for resistors and capacitors is the “home plate” design. The left aperture below (magenta) is a typical aperture reduction. The right aperture below (cyan) is the home plate pattern. Black being the component outline and terminals, and red being the original pads.

Horky_Fig1_Dec2017.jpg

Figure 1: Home plate design.

This is a very useful aperture design for mitigating solder balling and tombstoning. It can also be a difficult shape to describe, and convey where to apply it, to a stencil fabricator. Some large connector pins may benefit from oversizing the aperture to improve mechanical interconnect and ease inspection. Large heatsinks, such as those for DPAKs (Decawatt Package), can be divided into multiple apertures to reduce squeegee scooping and voids. Bowtie patterns can reduce solder balling on large gull wing pins.

I position the print image within my foil perimeter in the data, depending on the assembly type, and indicate the location for the stencil ID. My operators like the image forward of center for easier access, a better visual in process, and less ambiguous installation. We like to put both images of a double-sided board on the same stencil to reduce change over time. The distance between the two images needs to match your printer’s blade span and over travel distance.

Editing your own data also allows you to eliminate the check plot, further reducing your design cycle time. It also reduces the fabricator’s editing time, further improving their turn time.

Rather than spending time generating a document to describe the edits to your stencil fabricator and hoping they’ll get it right, make the edits yourself to get what you intended and improve your process.

Share

Print


Suggested Items

Collaboratively Creating Wearable Medical Products

05/28/2019 | I-Connect007 Editorial Team
Patty Goldman, Barry Matties, and Happy Holden recently spoke with David Moody and Rich Clemente of Lenthor Engineering along with Anthony Flattery and Amit Rushi—their customers at GraftWorx. They discussed a recent project and how they worked together to solve a difficult problem by designing a rigidized flex circuit for their product.

Green Circuits' Three Tips to Be a Well-prepared Customer

05/21/2019 | Nolan Johnson, I-Connect007
Nolan Johnson speaks with Joe Garcia, VP of sales and marketing at Green Circuits, about how they can help on both the front and back end of the process, their hidden gem—design services—as well as three tips to be a well-prepared customer.

The Perfect Job

05/06/2019 | Nolan Johnson, I-Connect007
After all the days and weeks invested into developing the schematic, the PCB design, poring over the data sheets and online libraries for component parts, and running the calculations for mechanical clearances inside the enclosure, you—designers—are ready to be done. You're ready for the next design challenge—not for a week or so perfecting the bill of materials and the design notes. And there's the rub. Find out why.



Copyright © 2019 I-Connect007. All rights reserved.