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DKL Metals Partners with NPL on Cu Dissolution
June 30, 2009 |Estimated reading time: 2 minutes
WEST LOTHIAN, U.K. DKL Metals Ltd. has become a project partner in the National Physical Laboratory (NPL) research project and report, "Measurement of Copper Dissolution in Lead-free Solder Alloys."
Ron Gow of DKL Metals stated, "The transition from tin/lead to lead-free solder has increased the tendency for copper dissolution in molten solders. This poses a potentially serious threat to circuit board reliability and is therefore an issue that affects manufacturers across all industries where electronics is incorporated. Whether it is for high-reliability applications or relatively inexpensive consumer products, it can result in undesirable implications for all."
DKL Metals asserts that the Nihon Superior tin/copper/nickel alloy SN100C provides a superior surface finish to the joints and dissolves the copper on the boards and components at a slower rate than silver-containing alloys. This is especially important on multiple reflow passes, as the industry had already identified issues with the total lack of copper on the pads during some rework operations. The company stated that most of its international companies were not prepared to share their data on this alloy with the industry in general, and therefore DKL decided to become involved with the NPL Project, testing of all the commonly used and commercially available lead-free alloys to the electronics industry.
The full report was compiled by Chris Hunt of the NPL, Davide Di Maio, also NPL and industry expert Bob Willis and consisted of findings from 15 project partners and references from important industry representatives. The report covers issues such as dissolution tests on copper wires and foils in a static and flowing solder, PCB design and tests on the effect of flow rate, tests of dissolution rates on commercial lead-free solder alloys, testing with different equipment, copper dissolution on different types of copper and printed circuit board trials, together with conclusions and references.
PCB land and plated through holes can be eroded or dissolved away in the presence of molten solder rendering the PCB non-functional. Significant dissolution can potentially occur with certain tin-rich alloys due to increased solubility of copper, which is further exacerbated by higher process temperatures. In order to determine the dissolution rate of copper in lead-free solders, a well defined and efficient technique had to be developed to compare solder performance.
The first phase of the project developed a measurement method for copper dissolution rates under a variety of conditions and with many different commercial and reference alloys. Here a special PCB design and erosion timing technique was developed. This methodology provided repeatable measurements that allowed the various experimental parameters to be isolated. These findings were tested in a second phase using a circuit board with assembled parts to assess the copper thickness after selective and hand soldering processes performed using various commercial alloys. The second part of this research aimed at verifying the potential impact on copper dissolution during soldering PCBs of the same type used in production, using single lead-free solder alloys and cored solder wires.
For a full copy of the report, visit www.dklmetals.co.uk and for a copy of the white paper contact Ron Gow of DKL Metals.