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www.us-tech.com
September, 2018 Production
HOW DO YOU CHOOSE THE RIGHT
SPRING-LOADED CONNECTOR?
How to Properly Treat Solder Paste
By Marc van Stralen, IMDES Creative Solutions
ponents — a good solder paste is the most important material in the SMT as- sembly and soldering process.
W
Preserving Solder Paste Solder paste must be kept in a controlled environment for it to remain
useful for a long period of time. It should be stored in a cool place and will last approximately 20 weeks at 39 to 50°F (4 to 10°C) in the refrigerator. At 68°F (20°C), solder paste’s useful lifetime is considerably reduced, to around 6 weeks. If the solder paste is used for dispensing, the syringes should be flipped regularly so that the paste does not sink down into the needle. It is also important to calculate the amount of paste needed and not order
too much. It is easy to buy too much paste and have it dry out in stock, ren- dering it unusable. The worst case is when the solder paste is stuck in the sy- ringe and cannot be dispensed by the plunger. Even if the paste looks good to the naked eye, it can still result in badly soldered PCBs, including poor joint quality, solder balling and voids. When
hen building a house, a strong foundation is critical, as well as reli- able materials to make the structure stable. A shoddy job can easily result in collapse. This is also true when reflow soldering SMT com-
START BY
CHOOSING THE RIGHT CONNECTOR PARTNER.
As new design challenges emerge every day, Mill-Max continues to lead the charge delivering high-quality, precision-machined spring-loaded contacts for critical design challenges. Now is not the time to fall behind, so it’s more important than ever to have an interconnect partner that understands today’s evolving technology and unique demands. But with hundreds of designs available, how do you decide which connector is right for you?
Our Spring-Loaded Connector industry white paper is a great place to start. Download a copy today:
mill-max.com/choose
If you require additional information, give our engineers a call, we’ll be happy to chat. We’re Mill-Max. This is what we do.
An automated screen printer prints solder paste through a stencil.
soldering BGAs, the connections cannot be inspected visually, since they are hidden under the package. Expensive X-ray inspection is currently one of the best ways to verify BGA solder joints. Never buy cheap paste whose production, batch or expiration dates are
not indicated or unclear. Also it is much better to place an annual order for solder paste from a supplier and have it delivered at various times and small- er quantities. This avoids having a large quantity of unused solder paste sit- ting around in stock.
Screen Printing Solder Paste All these considerations can be applied to solder paste for screen printing,
as well. Through screen printing, solder pads on the PCB are supplied with just enough solder paste for the reflow process. Solder paste consisting of 1.2 to 1.8 mil (30 to 45 µm) bullet-shaped granules and flux, forced through the openings of a specially manufactured stencil by a stainless steel squeegee is one way to de- posit paste precisely to PCB pad locations. The sensitivity of this part of produc- tion and the number of variables involved have a fundamental influence on the rest of the processes, including component placement and reflow. Of all the errors during SMT assembly, 60 to 70 percent of them can be
traced back to the printing process and the paste used. Never return leftover paste from screen printing back to its container, and make sure that the paste left on the screen has not been sitting there for too long. Paste can dry out on the screen, making it unreliable when forced through the holes of the stencil. In any construction job, getting
Run with us. Maximum Reliability. MillMaxMfg MILL-MAX MFG. CORP.
OYSTER BAY, NY 11771 • (516) 922-6000 MillMaxMfg
Mill-Max Mfg. Corp. • 190 PINE HOLLOW ROAD
There is no better way to reach the Electronic High Tech and Manufacturing Community than advertising in U.S. Tech.
www.us-tech.com.
the first steps right is the most impor- tant part of the process. In SMT assem- bly, the if the solder paste is not print- ed correctly, these errors cannot be fixed at a later stage. Manufacturing quality product starts with solder paste that is stored correctly and is
well taken care of. Contact: IMDES Creative Solu-
tions, Schulstrasse 21, D-48455 Bad Bentheim, Germany % +49-0-5924-997337 E-mail:
m.van.stralen@
imdes.de Web:
www.imdes.de r
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