Takashi Haramaki

Characteristics of press soldered joints by using resistance heating

In order to increase the strength of soldered joints, a novel press-soldering method was investigated. In this method, materials with low melting points and low strengths (mainly Pb) were discharged from the joint interface, and an alloyed layer of high strength was left. Copper-to-copper lap joints were press-soldered using a resistance heating apparatus. In this process, heating and pressure were applied simultaneously. The copper plate was presoldered using Pb-50Sn solder and the alloyed layer was formed. The tensile strength increased at a pressure above 45 N, and fracturing occurred in the copper base metal above a 75-N pressure load. The joints fractured in the copper base metal during 150 degrees C and 250 degrees C tensile testing and showed excellent thermal resistance. Changes in joint strengths after high-temperature heating (150 degrees C, 250 degrees C for 1000 h) were also considered.<<ETX>>

Characteristics of press-soldered joints by using resistance heating

In order to increase the strengths of soldered joints, a novel press-soldering method was investigated. In this method, materials of low melting points and low strengths (mainly Pb) were discharged from the joint interface and an alloyed layer of high strength was left. Copper-to-copper lap joints were press-soldered using a resistance heating apparatus. In this process, heating and pressure were applied simultaneously. The copper plate was presoldered using Pb-50 Sn solder, and the alloyed layer was formed. The tensile strengths increased at a pressure above 45 N, and fracturing occurred in the copper base metal above a 75-N pressure load. The joints fractured in the copper base metal during the 150 degrees C and 250 degrees C tensile testing and showed excellent thermal resistance. Changes in joint strengths after high-temperature heating (150 degrees C, 250 degrees C, 1000 h) are also considered. >

Peel Strength of microsoldered layer at leadframe microjoining. A study on microjoining of leadframe for LSI package (No.1).

Representative electric parts, LSI packages are turning to more fine pitch and more high pin count based on the demands of package size reduction which is coming from needs of smaller electric components. This reserch work has originated from high density LSI package surface mounting, including microjoining of leadframe on printed circuit board. In surface mounting of electric parts, solder past mass reflow line is applied to microjoining of fine pitch leadframe even less 0.5 mm pitch package outer lead on account of easy process controll and massproduction. But leadframe materials tend to smaller lead width and thinner by fine pitch photochemical etching technology propagation. This reserch work focused on reliability of fine pitch leadframe made with copper metal and Fe-42 mass% metal alloy surface mounted with solder past through long run aging.The result of this study have shown that fine pitch surface mount with solder paste (min. 0.3 mm pitch) is capable. But after high temperature aging (150°C×1000 h in air), Pb-60Sn eutectic microstructure of solder at leadframe microjoined is segregated to Pb rich and Sn rich large grain. And copper leasds become thin by high temperature reaction with solder. It was determined that copper was damaged in high temperature circumstance.

Durability evaluation of press-soldered joints.

Copper to copper lap joint was made by the resistance heating apparatus by which heating and pressure was applied simultaneously. The copper plate was pre-soldered and the alloyed layer was pre-formed by using Pb-50Sn solder.Tensile test of the joints was carried out at room temperature after heat test at 150°C or 250°C for 1000h, heat cycle test from -55°C to +150°C by 1000 cycles or salt spray test at 35°C for 1000h.All of these joints were fractureed at the base metal, copper.The strengths of the joints were as those of the joints which were brazed by using BAg-6.Although the joints made by press-soldering were heated at 150°C or 250°C the thickness of the alloyed layer was constant.