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www.us-
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Solving Power Supply Integration Issues Continued from page 56
Testing of the power supplies
and the end equipment for compli- ance with the required emissions lev- els can be costly, and most designers will need to appeal to test labs for help. Power supply manufacturers who provide support to design engi- neers can also help speed up the process of integration. For example, a lighting equip-
ment designer was having emissions problems he could not solve. The lighting equipment, with integrated power supplies, was analyzed. After performing a number of tests, it was found that a filter used in the equip- ment was adversely af - fecting the emissions per- formance. Once the filter was
removed and some of the wires re-routed, the emis - sions were brought into compliance. Fortun ately,
the
customer’s prob lem was solved, and the solution carried a bonus: a cost savings was realized since the company could eliminate the filter en - tirely from the design. Another potential
small as possible, which presents challenges related to heat dissipa- tion. Smaller power supplies require either more air cooling, or need to find a different way to dissipate the generated heat. Power supplies with higher con-
vection ratings will provide the most power in tight spaces, especially when air cooling is not possible. Another option is conduction cool-
ing. If the equipment has surfaces that can be used to pull heat out, some power supplies can be made to allow mounting to a heat conducting surface,
December, 2015
customer’s equipment was request- ed, as the internal temperature with- in the system was causing thermal shutdown of the power supply. Since there was no forced air cooling being provided, and not adequate venting for convection cooling, the addition of an aluminum plate to the power sup- ply allowed the heat to be conducted through the outside walls of the unit. This lowered the internal tempera- ture to an acceptable level, and quickened the customer’s completion of the design. In many cases, the integration
of a power supply into a product design is not complex. However, there are also many cases where
unforeseen issues arise and manu- facturers are called upon to help solve problems during the integra- tion of supplies into a design. A power supply manufacturer such as SL Power, who has the capability to provide local support and work with design engineers during integration is worth much more than parameters on a datasheet. Manufacturers who communicate with design engineers help them to move their designs for- ward quickly and confidently. Contact: SL Power Electronics,
6050 King Drive, Ventura, CA 93003 % 800-235-5929 fax: 805-832-6135 E-mail:
info@slpower.com Web:
www.slpower.com r
Solderability and Tinning: Does the Industry Know the Difference?
Continued from previous page
cent) are more aggressive than the tin-lead alloys.
The TU425 product family provides
output power of 300W convection or 425W with moving air.
issue is that of cooling. Many design- ers seek to keep their equipment as
and remove the heat by conduction. In one instance, an analysis of a
When to Use Solderability Testing
Solderability testing is a great drive in
tool to help determine if the surface finish of the selected components will provide the degree of wetting neces- sary for acceptable solder connections. If, for example, solderability testing results indicate less than optimal sol- derability, it could result in poor wet- ting and defective solder connections. This would then requires rework and additional processing. Solderability testing can also be used to determine the effects of storage conditions on the surface finish. By including accelerat- ed aging, the testing can also estimate acceptable storage life. This kind of testing can also be used to verify con- formance of the components as received from the vendor.
When to Use Tinning To ensure the best wetting of
solder connections, the terminations should be tinned just prior to the sol- dering process. Jim Raby, a pioneer of the industry and the founder of STI Electronics, once said, “Nothing solders like solder.” Tinning just prior to the soldering process ensures that the solderable terminations have an excellent solder coating that has not yet had the chance to form an oxide layer on the surface. This used to be common practice for the manu- facturing of high reliability electron- ic assemblies. When pre-tinning is accomplished just before the solder- ing process it eliminates the need for solderability testing. Tinning is also the best method
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to rework terminations that exhibit degraded solderability. Even severe- ly oxidized terminations can be re - worked by a hot solder dip tinning process replacing the oxidized sur- face with a pristine solder finish. Tinning in a tin-lead bath is one of the methods used for lead-free termi- nations that must be used in a tin- lead soldering process. The risk of whisker growth is greatly diminished by replacing the lead-free finish with a solder finish containing lead.
Lead-Free Soldering Compatibility
The 2003 rules — the “Waste
Electronic Equipment Act” (WEEE) and The Restriction of Hazardous Substances (RoHS) act went into effect on July 1, 2006. These rules have had an enormous effect on con- sumer electronics. Products for the defense and aerospace industries as well as medical electronics are “exempt” from these rules and contin- ue to use lead bearing solders and avoid the use of tin plating. The main reason for this refusal of lead-free materials is the risk of tin whiskers and other reliability problems inher- ent in lead-free soldering. While there is yet no definitive answer to what causes tin whiskers, as little as 1 per- cent lead added to pure tin materials drastically reduces their occurrence. Beginning July 1, 2006 RoHS
legislation restricted the amount of Lead (Pb), Cadmium (Cd), Mercury (Hg), Hexavalent Chromium (Cr6+), Polybrominated Bi phenyls (PBBs), and Poly brominated Diphenylethers (PBDEs) in electronic and electrical equipment. These chemicals present a risk to human health and the envi- ronment. Each EU member state adopts its own enforcement and implementation polices using the directive as a guide. Even though RoHS is a Euro -
pean directive, the RoHS directive has a global effect. The directive indi- cates that anything covered by RoHS entering the EU must be compliant, whether they include cables made in China, parts molded in the USA, or PCBs from Japan. If a product is eventually destined for the EU, it is impacted by RoHS. Contact: NJMET, Inc., 1240
Main Avenue, Clifton, NJ 07011 % 973-546-5393 fax: 973-546-1836 Web:
www.njmetmtl.com r
Vice President and Director of Oper - ations at NJMET, Joseph Federico has helped focus the company on elec- tronic component procurement, test- ing, up-screening, and counterfeit detection. He has met with distribu- tors around the world, as well as mil- itary and aerospace companies to raise the awareness of component counter- feiting. He would like to acknowledge Jim Raby, Dave Raby, Ray Cirimele, and Marietta Lemieus from STI Electronics, Inc., % 256-461-9191, for their special help with this article.
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