Journal of the Korean Institute of Electrical and Electronic Material Engineers (한국전기전자재료학회논문지)

The Korean Institute of Electrical and Electronic Material Engineers (한국전기전자재료학회)
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Evaluation of Bonding Properties of Epoxy Solder Joints by High Temperature Aging Test

고온 시효 시험에 따른 Epoxy 솔더 접합부의 접합 특성 평가

  • Kang, Min-Soo (Department of Mechanical Engineering, Chung-Ang University) ;
  • Kim, Do-Seok (Department of Mechanical Engineering, Chung-Ang University) ;
  • Shin, Young-Eui (Department of Mechanical Engineering, Chung-Ang University)
  • Received : 2018.08.08
  • Accepted : 2018.10.01
  • Published : 2019.01.01
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Abstract

Bonding properties of epoxy-containing solder joints were investigated by a high temperature aging test. Specimens were prepared by bonding an R3216 standard chip resistor to an OSP-finished PCB by a reflow process with two basic types of solder (SAC305 & Sn58Bi) pastes and two epoxy-solder (SAC305+epoxy & Sn58Bi+epoxy) pastes. In all epoxy solder joints, an epoxy fillet was formed in the hardened epoxy, lying around the outer edge of the solder joint, between the chip and the Cu pad. In order to analyze the bonding characteristics of solder joints at high temperatures, a high-temperature aging test at $150^{\circ}C$ was carried out for 14 days (336 h). After aging, the intermetallic compound $Cu_6Sn_5$ was found to have formed in the solder joint on the Cu pad, and the shear stress on the conventional solder joint was reduced by a significant amount. The reason that the shear force did not decrease much, even though in epoxy solder, was thatbecause epoxy hardened at the outer edge of the supported solder joints. Using epoxy solder, strong bonding behavior can be ensured due to this resistance to shear force, even in metallurgical changes such as those where intermetallic compounds form at solder joints.

Keywords

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Fig. 1. Shape of R3216 chip.

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Fig. 2. Shape of specimens (a) pure Sn58Bi solder specimensand (b) epoxy solder specimens.

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Fig. 3. Schematic diagram of shear test.

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Fig. 4. Cross-section images of primary specimens (a) SAC305 solder joint, (b) epoxy SAC305 solder joint, (c) Sn58Bi solder joint, and (d) epoxy Sn58Bi solder joint.

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Fig. 5. Intermetallic compound (IMC) layer in SAC305 and SAC305epoxy solder joint (a) before the test in plain solder joint, (b) afterthermal aging test in plain solder joint, (c) before the test in epoxysolder joint, and (d) after thermal aging test in epoxy solder joint.

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Fig. 7. Schematic diagram of shear test.

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Fig. 8. Graph of shear force drop.

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Fig. 9. Fracture surface of SAC305 and SAC305 epoxy solder joint(a) before the ageing test in plain solder joint, (b) after the ageing test in plain solder joint, (c) before the ageing test in epoxy solderjoint, and (d) after the ageing test in epoxy solder joint.

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Fig. 10. Fracture surface of Sn58Bi and Sn58Bi epoxy solder joint(a) before the ageing test in plain solder joint, (b) after the ageingtest in plain solder joint, (c) before the ageing test in epoxy solderjoint, and (d) after the ageing test in epoxy solder joint.

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Fig. 11. Graph of shear force drop.

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Fig. 6. Intermetallic compound (IMC) layer in Sn58Bi and Sn58Bi epoxy solder joint (a) before the test in plain solder joint, (b) after thermal aging test in plain solder joint, (c) before the test in epoxy solder joint, and (d) after thermal aging test in epoxy solder joint.

Table 1. Solder specification.

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