| FCT Assembly & Fine Line Stencil January 2005 News | Serving
the EMS provider since 1995 |
Article: |
COPPER
DISSOLUTION WITH LEAD FREE ALLOYS
One of the major issues with converting to a lead free soldering process is the concern about increased copper dissolution and how this affects the reliability of a soldered pad. In addition, an increase in copper dissolution rates could affect the ability to control the wave solder pot alloy. There have been indications from many major contract manufacturers who are in full production with lead free in Asia that excessive copper dissolution from the pads is a concern, particularly with the tin/silver/copper (SAC305) alloys. The pictures below illustrate what can happen if the copper dissolves too quickly from the pad. This is a wave soldered pad and even at a quick 3 second contact, the copper has been dissolved to an extent as to affect the integrity of the joint.
To determine the speed of copper dissolution, a number of laboratory tests have been performed on the tin/silver/copper (SAC305), tin/silver/copper/bismuth (Alpha SACX0307), and SN100C. The table below includes results of a test in which a thin (0.48mm) copper wire under tension is immersed in molten solder at 255°C and the time to breakage is measured. It can be seen that the SN100C not only dissolves copper slower than the Alpha SACX0307, it also dissolves copper slower than 63/37 tin/lead solder.
The chart below illustrates the amount of copper dissolving at a given time in molten solder at 270°C. Again, this shows the SN100C not only dissolving copper slower than all other lead free alloys but also slower than 63/37 tin/lead.
Many of the issues with converting to a lead free process will not be evident until the process is in place. Please be aware that just because a particular alloy is popular in Asia, that does not necessarily mean that it is the best option in your application. As the assemblies soldered with lead free become more complex, the reliability of the joint becomes more important and a reduction in the copper pad can play an important role in maintaining the integrity of the joint. Consider all requirements before choosing a lead free alloy.
CHUBU HIGH TECHNOLOGY SERVICE SN100C Use on Mixed Technology Computer Mother Boards The use of Nihon Superior's lead-free Sn-Cu-Ni solder SN100C is rapidly expanding and producing successful results. In addition to having a joint reliability at least as good as that of conventional tin-lead eutectic solder, SN100C ensures that joints have a bright, smooth finish. Also, since it does not contain precious metals, and therefore offers cost benefits, it has a wide range of applications. Efforts to introduce lead-free materials in the electronics industries in Japan and abroad have been increasing at fever pitch. In our series on SN100C users, we spoke with Chubu High Technology Service (Toyokawa City, Aichi Prefecture), a company that uses SN100C for computer circuit boards. Chubu High Technology Service is a wholly owned subsidiary of Hitachi Ltd. Its headquarters are located at Hitachi's Toyokawa plant, the production center for Hitachi computers and servers. The company oversees manufacturing activities ranging from production planning to materials procurement, production, and quality assurance. Hitachi was the first in the industry to partially introduce lead-free solder on the circuit boards of its notebook computer, FLORA220CX, in February 1999. They introduced a lead-free reflow process for their 220FX circuit boards in April 2000, and then introduced SN100C into their wave soldering process in September that same year. Lead-containing solder has been completely eliminated from the printed circuit boards used in all of the new models produced at the Toyokawa plant since March 2002. Also notable is the company's simultaneous elimination of halogen-based laminate materials in its efforts to prevent the production of dioxins during disposal and incineration of scrapped electronic equipment. The 220FX motherboard has 1,000 surface mount components and 10 inserted components. The surface mount components are reflowed using a Sn-Ag-Cu solder, while SN100C is used for the inserted components. "SN100C was selected not only for its cost and joint reliability, but also because it does not suffer surface finish defects such as wrinkling," says Mr.Hiroshi Tokoro, PK Center Manufacturing Engineer Group Unit Leader of Chubu Hi-Tech Service. This group is currently expanding its range of applications beyond computers into other products with wave soldered boards. Meanwhile, Chubu High Tech is hoping to share its lead-free know-how with other companies by offering a unique SN100C solder evaluation contracting service. Its menu of support services for other companies includes the trial production of large printed circuit boards, production services on small-quantity and larger projects, and mounting design. Chubu High Tech is increasing its contracting experience by performing services for manufacturers of business machines and machine tools in the Chubu region. Interviewed by Nikkan Kogyo Shimbun. 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. |
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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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