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Article
Publication date: 1 April 2001

Yoshiharu Kariya, Colin Gagg and William J. Plumbridge

Considers the effect of low temperatures on the characteristics of lead‐free alloys based upon tin, which is the most popular basis for the new alloys.

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Abstract

Considers the effect of low temperatures on the characteristics of lead‐free alloys based upon tin, which is the most popular basis for the new alloys.

Details

Soldering & Surface Mount Technology, vol. 13 no. 1
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 3 July 2007

Mi Jin Kim, Y. (Norman) Zhou and Jae Pil Jung

This paper seeks to decrease the soldering temperature of capacitors using Sn‐Bi plated Sn‐3.5 wt%Ag solder.

407

Abstract

Purpose

This paper seeks to decrease the soldering temperature of capacitors using Sn‐Bi plated Sn‐3.5 wt%Ag solder.

Design/methodology/approach

Sn‐Bi layers were electroplated on Sn‐3.5 wt%Ag solder. As soldering examples, type 1608 capacitors electroplated with Sn, and printed circuit boards (PCBs) with a surface coating of electroless‐plated Ni/Au, were selected. Sn‐3.5Ag foil coupons plated with Sn‐95.7 wt%Bi were inserted as solder between the capacitors and the lands on the PCBs. The samples were reflowed at 220°C, which is below the normal reflow temperatures of around 240 ∼ 250°C used with Pb‐free solders. During heating, Bi in the plated layer diffuses into the Sn‐3.5Ag core solder resulting in a transient decrease in soldering temperature based on the concept of transient liquid phase bonding.

Findings

The joints made with the Sn‐95.7%Bi plated Sn‐3.5Ag solder at 220°C showed good appearance, and evidence of significant Bi segregation was absent in the microstructure. The shear strengths of the capacitor joints bonded with Sn‐95.7%Bi plated Sn‐3.5%Ag solder were approximately 5,000‐6,000 gf. After 1,000 thermal cycles between −40 and +125°C, the shear strengths of the joints decreased approximately 5‐10 percent from the strengths in the as‐reflowed state for all plated solders. This confirmed that the soldered joints were stable and not significantly degraded by thermal cycles.

Originality/value

Reduced temperature soldering using Sn‐Bi plated Sn‐3.5%Ag solder was applied to attach capacitors to PCBs. In a production application, the foil coupons could be replaced by pre‐solder on the PCB pads.

Details

Soldering & Surface Mount Technology, vol. 19 no. 3
Type: Research Article
ISSN: 0954-0911

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