Ask the Experts
January 2, 2008 - Updated
January 2, 2008 - Originally Posted

Zinc in solder

What is the role of Zinc in solder material composition? What is the right ratio of Zinc to other alloys? Is there any standard composition that we should look for?


Expert Panel Responses

Zinc has always been considered a contaminant in solder. As quoted from Manko's Solders and Soldering, McGraw Hill, page 68. "Zinc. This material has small solid solubility in tin and no apparent solubility in lead. No intermetallic compounds are formed with either tin or lead. The addition of zinc is reported to be very detrimental to the solder alloy. As little as 0.005 per cent of zinc is report to cause lack of adhesion, grittiness, and/or susceptibility to failure during solidification. Little zinc is encountered in electronic soldering to endanger the properties of solder pots." From R.J. Klein Wassink, Soldering in Electronics, Second Edition, Page 73, Para Contaminated Solder, he states "Zinc contamination of solder causes strong dewetting. Although the dewetting mechanism in this instance had not be unraveled completely, a similarity is found between this cases and that discussed in the preceding text, Figure 2.36 show a dewetted copper plate with zinc-contaminated solder (0,3% by mass). Part of the surface (not shown) is covered by droplets with an appearance similar to that of the droplets in Figure 2.31. On the dewetted region solder is obviously present, and again many non-wetted spots are found . On the other hand the surface show features, such as that present at the top-left of the picture, resulting from broken oxides skins. On page 194, 4.7.4 Alloys with Higher Strength Values it does mention "The alloy lead90 cadmium9 zinc1 has a higher fatigue resistance than eutectic tin-lead solder [Denlinger et al] but this alloy has several technological disadvantages, such as the high melting range of 238-260C" With the RoHS requirements, this alloy would not be allowed due to constituent of Cadmium. So from my sources Zinc is not a good thing to have as an element in a soldering alloy. From a search on Wikipedia on Brass, the following appears. Brass is any alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.[1] Note that in comparison bronze is principally an alloy of copper and tin.[2] As can be seen, zinc does exist in some products that we may solder to during the process of making electronic products and cable. Brass connectors are not uncommon for coaxial cable, which is why we need to take caution when soldering those products. I hope this help your understanding of having Zinc in the solder alloy and the problems it may cause.

Leo Lambert
Vice President, Technical Director
EPTAC Corporation
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.

Zinc is a undesirable element in solder alloy so it has no role in the alloy composition. The max amount of zinc as stated by IPC-STD-006 is .003 %. The standard alloy mix is Sn63/Pb37 plus some trace elements.

IPC-STD-006 gives the max percentage of all trace elements. Zinc in high levels in solder alloy has a corrosive effect to stainless steel and titanium and can quickly destroy these metals. Zinc will also affect the liquidus temperature of the alloy and the quality of the solder joint. It would be interesting to know why you are asking this question about Zinc in solder.

Greg Hueste
Senior Applications Engineer
Speedline Technologies
Greg joined Electrovert in February 1984. Based out of the Electrovert applications laboratory in Camdenton Missouri, Greg has been in the process applications support role since 2000. His primary responsibilities include providing process and machine applications support for the wave soldering lines as well as process, machine and operations training. He also provides applications support for the reflow and cleaner lines. Greg is a PBET certified trainer and holds two patents on wave solder nozzle design.
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