Relationship between the Reduction Behavior of Copper and Tin Oxide Films by Formic acid and Solder Wettability

Abstract

2 Experimental Method 2. 1 Materials Copper plates (purity: >99.96%, size: 20 × 20 × 2 mm) and solder foils (SnAg3. 0 Cu 0.5, size: 10 × 12 × 0.07 mm) were used as samples for analyzing the oxide film and measuring the oxide film thickness. Solder foils (SnAg3. 0 Cu 0.5, size: 5 × 5 × 0.07 mm) and solder balls (SnAg3. 0 Cu 0.5, size:φ1.5 mm) were used for the evaluation of wettability. The rust preventive agent and working oil used during the processing of copper plates were completely removed by immersion and degreasing by ultrasonic waves (using 1-bromopropane). Both copper plates and solder foils were stored in air for six months or more after processing, and native oxide films were initially formed. Formic acid (KANTO CHEMICAL CO., INC.; special grade, purity: > 98%) was used as the reducing agent, and N2 gas (99.99% purity) was supplied using an N2 cylinder. CuO (purity 99.9%) and Cu2O (purity 99%) manufactured by Kojundo Chemical Laboratory Co., Ltd. were prepared as reference samples for electron energy loss spectroscopy (EELS). SnO (purity 99.5%) and SnO2 (purity 99.99%) were used as reference samples for X-ray photoelectron

Reduction of copper oxide by formic acid in a narrow gap under various conditions

“…[21][22][23][24][25][26][27][28][29][30] In this study, we combined a spectroscopic ellipsometer with an originally designed vacuum chamber to study in situ the reduction of oxide films on copper plates and solder surfaces during formic acid exposure. 31,32) Furthermore, the data on the relationship between the reduction rate and copper plate temperature was obtained to determine the activation energy of the reduction of the copper oxide film by formic acid. Moreover, the reduction rate increased with increasing formic acid partial pressure.…”

Reduction process of copper oxide film by formic acid

“…In situ analysis of the oxide film on a copper plate surface and a solder surface when exposed to formic acid was performed by combining a spectroscopic ellipsometer and an in-house designed vacuum chamber. 41,42) In this study, detailed data on the relationship between the reduction rate and the copper plate temperature and formic acid partial pressure were obtained by in situ spectroscopic ellipsometry analysis. In addition, the rate-determining step and the mechanism involved in the reduction reaction of the copper oxide film with formic acid were considered.…”