Ask the Experts
March 11, 2019
Initial Screen Print Test Board
Is it recommended to print one cycle before printing the first production board? I could use a scrap board or blank plastic card for the first print.
Expert Panel Responses
It is not a bad idea. It will depend much on the quality of the solder paste. Some pastes are ready to print right out of the jar/cartridge. Some need a few knead strokes to get them going.
Technical Support Engineer
Kay Parker is a Technical Support Engineer based at Indium Corporation's headquarters in Clinton, N.Y. In this role she provides guidance and recommendations to customers related to process steps, equipment, techniques, and materials. She is also responsible for servicing the company's existing accounts and retaining new business.
This is a good practice in order to set your printer when you run a PCB for the first time. Once your printer parameters are set you shouldn't have to do a one cycle print before production. Always have your print inspected by an AOI system for quality of solder deposition in critical areas such as fine-pitch and micro-BGA's. I'd also recommend to set the printer with a production PCB. Refrain from using blank plastic cards since they do not provide you with complete picture of your pad landscape.
Senior Manufacturing Engineer
Edithel is a chemical engineer with 20 year experience in manufacturing & process development for electronic contract manufacturers in US as well as some major OEM's. Involved in SMT, Reflow, Wave and other assembly operations entailing conformal coating and robotics.
The important issue is the accuracy of the alignment of the stencil to the board. If the printer does not have camera capability for alignment, then I would suggest running a test alignment board. I would not run a plastic card, as it may not have the artwork on the card. I've seen people use a regular board and apply a removable film on the board, so the accuracy can be checked to the physical artwork. If it is aligned then the removable film can be removed and the process can be started.
If you do use a board, be it a scrap board or not, make sure to clean it properly to get all the solder paste off the board and out of the plated through holes.
Vice President, Technical Director
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.
Yes. Good practice.
Vice President Technology
For over 18 years, Dr. Coleman has been the vice president of technology for Photo Stencil, working closely with customers to understand their printing requirements. His efforts have resulted in several new stencil products.
Yes it is a good idea to print 1 or two blank/scrap circuit boards before printing the first production board. This helps the solder paste to wet and flow properly through all of the stencil apertures.
Tony has worked in the electronics industry since 1994. He worked as a process engineer at a circuit board manufacturer for 5 years. Since 1999, Tony has worked for FCT Companies as a laboratory manager, facility manager, and most recently a field application engineer. He has extensive experience doing research and development, quality control, and technical service with products used to manufacture and assemble printed circuit boards. He holds B.S. and M.B.S. degrees in Chemistry.
This depends on the component sizes and paste deposition required. If you are placing any 0.4mm BGA's or 0201 components then I would recommended first board printing. This is purely because volume for these types of components are critical. Typically, solder paste has air pockets and bad roll of the first print, you will find solder paste skips, voids which effects the total volume required on a pad. If you have an SPI, then I would low volume can be flagged, hence no need for first board printing even if you are using .4mm BGA's or 0201 components.
Process Engineering Manager - Electronics
Altech UEC, South Africa
Currently with Altech UEC and responsible for technology road map in PCBA electronic manufacturing and technical support for PCBA electronic manufacturing for Altech UEC and its JDM's. Over 7 years in SMT, Radial Insertion, Wave solder & Test Applications.
Many modern pastes will print better if they are subjected to a kneed cycle (2 to 4 sweeps of the squeegee) prior to printing. This process achieves two things one helps to condition the solder paste, optimising its rheology, wetting out the squeegees and making sure that the bead of paste is of even size across the squeegee and extends beyond the end of the apertures. Two it ensures that the apertures of the stencil are fully wet out, this is important in determining the release of the paste from the stencil. One common solution to this problem is to perform a double sweep for the first print, this invariably produces a usable board with good print volumes.
Senior Applications Chemist
Dr. Poole is a Senior Applications Chemist in Henkel Technologies, electronics assembly materials application engineering group. He is responsible for all of Henkel's assembly products including soldering products, underfills, PCB protection materials, and thermally conductive adhesives.
There are a couple reasons why it might be a good idea:
In the end, whether this gives you a benefit depends on how well engineered your stencil printing process is, and how close to the edge of the printing envelope you are. If you are pushing the limits of acceptable aperture ratios, you may find that an initial print on scrap material is of benefit. A lot depends on the specific paste being used as well. Some pastes exhibit a larger difference from first to second print than others.
- It will get the paste roll worked (sheared) a little, and get the paste physically into the "roll" shape and more evenly distributed across the squeegee.
- Get the stencil walls wetted with flux, which is the "normal" condition.
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.
It depends on what is the population on the board. The smaller the parts/apertures, the higher risk of paste deposit deficiencies. This is not necessary, however it is not a bad idea if you can do that.
Engineering and Operations Management
Georgian Simion is an independent consultant with 20+ years in electronics manufacturing engineering and operations.
Contact me at email@example.com.
The experts seem to be unanimous, and I agree it is a good idea. Not only for the reasons stated, but if you have ever cleaned a stencil you know that the flux residue on the surface of the stencil is very sticky, and this is what helps the paste to "roll" properly. You may need one or two passes to obtain that flux residue before the paste begins printing properly without sliding in a pile.
Richard D. Stadem
Richard D. Stadem is an advanced engineer/scientist for General Dynamics and is also a consulting engineer for other companies. He has 38 years of engineering experience having worked for Honeywell, ADC, Pemstar (now Benchmark), Analog Technologies, and General Dynamics.