More Stencil Questions (and the Answers!)


Reading time ( words)

My March The Short Scoop column, "10 Common Stencil Questions," brought in a slew of new questions from customers. Do you know the answers?

1. What are my fiducial choices and how do they differ?

Yes, stencils require fiducial markings to make sure the stencils are aligned correctly to properly print the pattern, as most people know. What they might not know is that there are actually several types of fiducials, and when you select a stencil, you must choose one of them.

The fiducial choices available today depend on the stencil manufacturer you use and/or your own requests, but truthfully, there really are only two predominate types. One is half-etched and filled, which have an etched pocket in the stencil at the fiducial location that is then filled with a black epoxy. Ultimately, these offer one of the strongest contrasts for the visual printer cameras, but they are an older technology and often, the epoxy falls out at the least opportune time. 

The other predominate type is a laser tattooed fiducial, which is a relatively newer technology. These are applied by a laser (usually the same one that cuts the apertures for a laser stencil).  In this technology, the laser truly burns the fiducial to the stencil.  The benefits are that it lasts forever and the epoxy doesn’t fall out. Laser tattooed fiducials provide the tightest location tolerance of any fiducial and most companies are moving toward this technology. It is imperative to note, however, that the darkness of the laser fiducials have varying contrasts from one stencil to another. This is usually due to the material type, the pattern density of the stencil, laser type, and several other factors. I mention this because some printers struggle with the contrast that is less than what they might have had previously in the half-etched and filled fiducials.

2.  What CAD information and files are needed to make my stencil and how will I receive my check plots?

These are very important questions so that manufacturers know what to expect and don’t waste time or effort preparing something that isn’t usable by the stencil manufacturer. Additionally, they don’t have to go back to a format that is different from what is usually done. We use IGI and Valor, which are software systems that can custom design each stencil.

Read the full column here.


Editor's Note: This column originally appeared in the July 2014 issue of SMT Magazine.

Share

Print


Suggested Items

Practical Implementation of Assembly Processes for Low Melting Point Solder Pastes (Part 1)

07/16/2019 | Adam Murling, Miloš Lazić, and Don Wood, Indium Corporation; and Martin Anselm, Rochester Institute of Technology
Since 2006 and the implementation of the RoHS directive, the interest in bismuth-tin solder alloys—whose melting point around 140°C is very desirable because it allows for the use of lower temperature laminate materials and reduces thermal stress on sensitive components—has only increased as the industry has searched for Pb-free alternatives to the chosen standard, SAC305, which melts at considerably higher temperatures than the incumbent tin-lead alloys.

Surface Treatment Enabling Low-Temperature Soldering to Aluminum

07/15/2019 | Divyakant Kadiwala, Averatek Corporation
An increasingly popular method to meet the need for lower cost circuitry is the use of aluminum on polyester (Al-PET) substrates. This material is gaining popularity and has found wide use in RFID tags, low-cost LED lighting, and other single-layer circuits. However, both aluminum and PET have their own constraints and require special processing to make finished circuits.

Size Matters: The Effects of Solder Powder Size on Solder Paste Performance

07/08/2019 | Tony Lentz, FCT Assembly
Solder powder size is a popular topic in the electronics industry due to the continuing trend of miniaturization of electronics. And the question commonly asked is, "When should we switch from Type 3 to a smaller solder powder?" Read more to find out.



Copyright © 2019 I-Connect007. All rights reserved.