| FCT Solder & Fine Line Stencil August 2004 News | Serving
the EMS provider since 1995 |
Notice: Nihon Superior Joins NEMI! Article: Options For Lead Free Tinning Operations |
NIHON SUPERIOR JOINS NEMI! In an effort to work closer with North American electronics manufacturers in their quest to switch to a lead free process, our lead free partner, Nihon Superior has joined the National Electronics Manufacturing Initiative (NEMI). NEMI is an industry-led consortium of more than 60 electronics manufacturers, suppliers and related organizations. Their mission is to assure leadership of the global electronics manufacturing supply chain. The formal announcement will be made at the September 15 meeting and Nihon Superior plans to be actively involved in the NEMI Lead Free Wave Solder project chaired by Dr. Denis Barbini, Vitronics Soltec. The status of the various lead free NEMI projects can be reviewed at www.nemi.org. OPTIONS FOR LEAD FREE TINNING OPERATIONS One of the last remaining requirements for a complete lead free process is the sourcing of components with lead free finishes. The component manufacturers have had to spend the most time and money on requalify their products with lead free finishes and to withstand the higher temperatures of a lead free process, particularly with the surface mount components being subjected to the higher reflow temperatures. For through hole components, one of the popular lead finishes historically has been a tin/lead solder dip coating. This process is fast, highly automated and relatively cheap. With the elimination of lead, this solder dip process will be replaced with the lead free alloys being considered for typical wave solder application. These alloys include tin/silver/copper, tin/copper, tin/silver, and the nickel stabilized tin/copper, SN100C. It would be ideal if the alloy chosen could be used with the same parameters as the tin/lead process. In order to be a successful replacement, the lead free alloy needs to have similar copper dissolution characteristics and offer a stable solder coating with a long shelf life. Automated lead tinning equipment is similar to wave solder machines in the solder process so many of the characteristics that make a solder perform well in wave soldering will be useful in lead tinning. The flux is typically applied by wave but there may be very little preheat. The solder immersion time is usually longer to make up for the lack of preheat. The solder will typically be applied using a solder fountain, which tends to dross similar to wave machines. A major advantage to the SN100C is the low dross production in a wave or fountain application. The SN100C tends to dross as much as 50% less than SN63 while the other lead free alloys tend to dross as much as twice the level of SN63. Since there is no requirement to fill a through hole and the leads tend to heat quicker than a p.c. board, the length of time in contact with the solder does not have to be extended. The temperature of the solder also can be maintained in the range of 250°C to 260°C. A major concern with switching a solder pot from SN63 to a lead free alloy is the rate of copper dissolution. Lead free alloys tend to dissolve copper much quicker than tin/lead alloys. Experience in wave soldering with SN100C indicates that it dissolves copper much slower than the other lead free alloys and even slower than Sn63. A test was performed in which a 0.44mm copper wire was fluxed and immersed in solder held at varying temperatures. The diameter of the copper after cross sectioning was measured over time. In all cases, the SN100C dissolved the copper slower than the tin/3% silver/.5% copper (SAC305) and even less than SN63 tin/lead. The graph below illustrates the results at 250°C. the SN100C dissolves copper approximately 4 times slower than SAC305 and 2 times slower than SN63 at 250°C.
When you consider the lead free options for lead tinning application, the SN100C is proving higher desirable, not only compared to the other lead free alloys but it appears to have advantages over the SN63 tin/lead alloy. Samples of SN100C are available if you would like to evaluate it as a lead-tinning alloy. Please contact us. TOKO, INC. TINNING EXPERIENCE
Toko, Inc. developed the first IFT (Intermediate Frequency Transformer) for transistor radios in 1956, and it has been their main business. Since it’s development, Toko has widened their field of products but still maintains the top market share of coil products. Toko started the evaluation of lead free for the coil products in April 1997. The insulated copper wires on the coil’s external terminal are required to be tinned. To remove the insulation, it is dipped into a pot of high temperature tin/lead solder at 400°C. This strips the insulation and solder coats the copper wire. At this high temperature, copper erosion of the wire occurs which can weaken the copper wire as it loses thickness. In considering a lead free alloy replacement, Toko evaluated Tin-Copper, Tin-Silver, and Tin-Silver-Copper. Based on their test criteria, they chose the nickel stabilized tin/copper eutectic- SN100C. Commercial production with SN100C began in April 2000. One of the issues recently is the fact that coils are getting smaller which requires finer copper wires. These wires have a much higher potential to dissolve at the high soldering temperatures required to remove the insulation. Fortunately, Toko has found that the SN100C can be used on wires even as small as 20 microns (0.008”). “If such ultra fine wires as this,” said Mr. Yasuo Nagamine, the Manufacturing Manager for the No. 2 coil division, “are dipped into high temperature solder, it could be vanished in the pot rather than thinned. We are making mass production with this new solder material (SN100C) for more than two years, we can find no faults in solderability, using machines and keeping the quality of solder joints.” Toko has decided to schedule the adoption of SN100C for all lines. Asking the customer’s opinion, Toko is keen to adopt SN100C to meet the environmental goals they have set. SN100C has been patented by Nihon Superior and is offered worldwide through licensed manufacturers including FCT Solder for North America. We offer SN100C for wave solder and lead tinning application and SN100CL for lead free hot air solder leveling (HASL) of P.C. Boards. We will be including in future newsletters, many of the advantages our current customers have discovered in switching to SN100C as their lead free alloy of choice and we welcome your comments and questions. We look forward to working with you to make your transition to lead free as successful as possible. |
For more information about our products, please visit our web sites at www.finelinestencil.com for stencil products and www.fctassembly.com for solder products. All files for stencils, templates and PCB carriers should be sent to sales@finelinestencil.com to assure immediate attention. |
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