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The European Commission has proposed that the third draft of the Electronic Equipment Disposal Order stipulates that hazardous substances such as lead Pb, cadmium Cd, mercury Hg, and hexavalent chromium Cr are strictly prohibited in 2004 waste. In Japan in Japan, the Household Appliances Recycling Act was enacted in 1998. Since 2001, manufacturers have fulfilled their obligation to collect used home appliances. According to this bill, Japan’s home appliance and information equipment manufacturers have started activities to reduce lead use. Against this background, the development of lead-free soldering technology and the corresponding tin-copper Sn-Cu alloy electroplating technology are strongly demanded.
Lead-free solder plating technology requirements
With respect to lead-free solder plating and electrolytes, besides the fact that lead-free materials are not allowed to be used, it is more difficult to achieve the same valuable features as Sn-Pb plating layers that have been used in the past. Specific performance requirements are as follows: (1) Environmental safety - No substances such as lead Pb harmful to human health and environmental pollution are allowed; (2) Precipitation stability - Obtain uniform outer surface and uniform alloy Ratio; (3) Solder Wettability - When subjected to heat resistance test and high temperature, high humidity test, the wettability of the solder only allows a slight degree of deterioration; (4) inhibit the generation of metal whiskers; (5) Welding Strength Adhesion - Joint reliability with solder material; (6) Flexibility - no fracture; (7) Non-contaminated flux tank; (8) Low cost; (9) Good workability - - Mainly refers to easy management of electrolysis; (10) Long-term reliability - Even if the electrolyte is used for a long time, it can ensure the stability of the electroplating layer; (11) Drainage treatment - Without special chelating agent (Chelate), available And cohesive precipitation treatment methods remove heavy metals.
In the selection of lead-free solder plating technology, a comprehensive analysis of the above factors must be considered. Select the Sn-Pb plating performance of lead-free solder plating technology, select the reason for Sn-Cu (alloy solder) electrolyte as lead-free solder plating technology, now There have been many studies, such as attempts to replace Sn-Pb plating that has been used with Sn-Zn, Sn-Bi, Sb-Ag, and Sn-Cu plating. However, these lead-free plating technologies are also short and long and not perfect. For example, the advantage of Sn electroplating is low cost, and there is indeed a force method of electroplating tin used in electronic devices, because it is a single metallic tin, and of course there is no problem of managing the ratio of electroplated alloy. However, the disadvantages of Sn plating are prominent, such as the generation of metal whiskers (Whisker) and the deterioration of solder wettability over time. The length of Sn-Zn electroplating is low in cost and melting point, and the fly in the ointment is difficult to weld in the atmosphere, and welding must be performed in nitrogen. Sn-Bi electroplating has the advantages of low melting point and excellent solder wettability. The disadvantages are also enumerated: Bi is a brittle metal, Sn-Bi plating containing Bi is prone to cracks, and the assembled device lead and circuit board are soldered. Liftoff, more problematic, is the displacement of Bi3+ ions in the electrolyte on the Sn-Bi alloy anode or plating. The advantages of Sn-Ag electroplating are that the bonding strength and heat-resistant fatigue characteristics are very good. The disadvantage is that the cost is high, and Ag substitution and deposition phenomena occur on the Sn-Ag anode and the Sn-Ag plating layer.
The above-mentioned lead-free electroplating technology has excellent characteristics, and there are also many issues for further study, and it is too early to be practical. For this reason, Sumimura Industrial Co., Ltd. believes that Sn-Cu electroplating is the most promising alternative to Sn-Pb electroplating and that it can be developed into practical technology, and decided to develop Sn-Cu electrolyte. Regarding the Sn-Cu plating characteristics, it has good wettability except for a slightly higher melting point (Sn-Cu eutectic temperature 227[deg.] C.). Low cost, no convection weld tank, and can inhibit the formation of metal whiskers.
Sn-Cu alloy solder development Standard Sn/Sn2+ electrode potential is -0.136Vvs. SHE (25°C), however, Cu/Cu2+ is +0.33V, and the potential difference between the two is relatively large. In a simple salt-like electrolyte, copper Cu is easily precipitated preferentially.
Moreover, when soluble Sn anodes or Sn-Cu alloy anodes are used, precipitation precipitation occurs due to the displacement reaction between Cu2+ ions in the electrolyte and the Sn of the anode. Table 1 Standard Electrolyte and Operating Conditions (obtaining Sn-lwt% Cu Plating Because of the close proximity of Sn2+ in the electrolyte and the precipitation potential of Cu2+, there is a need for a complexing agent that inhibits the precipitation of copper Cu. By studying various complexing agents, Sn- Cu electrolyte formulation, which can form an alloy of Sn and Cu and can suppress the displacement deposition on the copper Cu anode.In the basis of this electrolyte, developed the Sn-Cu alloy electrolyte with excellent coating characteristics "Soft Alloy "GTC" will be described in detail below.
As we all know, tin-lead (Sn-Pb) alloy solder can be excellent, and it is widely used in the field of electronic component assembly. However, it is very regrettable that lead in Sn-Pb is harmful to the environment and human health, and activities that restrict the use of lead-containing electronic materials have been officially launched.