Search results

1 – 1 of 1
Per page
102050
Citations:
Loading...
Access Restricted. View access options
Article
Publication date: 29 May 2018

Shou-Jen Hsu and Chin C. Lee

The purpose of this research was to develop a new process to bond silicon (Si) chips to low carbon steel substrates using pure tin (Sn) without any flux.

95

Abstract

Purpose

The purpose of this research was to develop a new process to bond silicon (Si) chips to low carbon steel substrates using pure tin (Sn) without any flux.

Design/methodology/approach

Iron (Fe) substrates were first electroplated with a Sn layer, followed by a thin silver (Ag) layer that inhibits Sn oxidation thereafter. It is this Ag capping layer that makes the fluxless feature possible. Fluxless processes are more environmentally friendly and more likely to produce joints without voids. The Si chips were deposited with Cr/Au dual layer structure. The bonding process was performed at 240°C in vacuum. The Sn joint thickness was controlled by spacers during the bonding. Scanning electron microscopy images on cross sections exhibited quality joints without visible voids. Energy dispersive X-ray spectroscopy analysis was used to detect joint compositions.

Findings

It was revealed that the Sn layer was bonded to a Si chip at the Cr–Sn interface and to the Fe substrate by forming an FeSn2 intermetallic compound (IMC). The IMC is only 1.1 to 1.5 µm in thickness. Thin IMC is highly preferred because IMC deforms a little in accommodating the coefficient of thermal expansion (CTE) mismatch between Si and Fe. Shear test results showed that the fracture forces of the samples passed the military criteria by a wide margin.

Originality/value

This new fluxless bonding process on Fe should make Fe or low carbon steel a more likely choice of materials in optical modules and electronic packages.

Details

Soldering & Surface Mount Technology, vol. 30 no. 4
Type: Research Article
ISSN: 0954-0911

Keywords

1 – 1 of 1
Per page
102050