In an effort to further reduce costs and the adverse properties of silver, a silver-free alloy, SN100C (melting point 227☌), was released in the late 1990’s. This alloy is a nickel (Ni)-stabilized Sn/Cu alloy providing improved wetting and solder flow. It was often confused with the fire retardant used in industry, antimony trioxide, a suspected carcinogen. However, the antimony content was a concern due to a misperception that it had high toxicity profile. This SAC305/Sb alloy had a lower melting point (217☌) than Sn/Ag (221☌) and lowered the silver creep and cost problems by reducing the silver by 0.5-1%. The SAC alloys remained the preferred lead free alternatives until the surge in silver prices. Concurrently, AIM patented and released the CASTIN alloy. SAC305 is tin, 3% silver and 0.5% copper.) All SAC alloys share the common disadvantage versus the tin/lead they replace:ġ) Increased cost due to the silver contentĥ) Potential damage to existing wave solder equipment (Note: the first number refers to silver content followed by the last number, which is the copper content. The three leading commercialized SAC alloys were introduced as SAC305, SAC387, and SAC405. In early tests, Sn/Cu exhibited inferior reliability in thermal cycling (-65+125C) and was prone to in-process wetting issues. Initial selection criteria deemed SAC to be the more reliable option. The most obvious difference from the industry standard was the substantially higher melting temperature of 221☌ versus 183☌ (Sn63/Pb37).Īlthough Sn/Ag had been used extensively in hybrid electronics, concerns over silver migration and silver creep drove the industry to investigate Sn/Cu and (S)n/(A)g/(C)u (SAC) alloys. When lead-free solders were first introduced to the electronics industry in the early 1990’s, the tin-silver alloy composed of Sn96.5/3.5Ag was the first investigated.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |