Effects of commercial no-clean flux on reliability of fine pitch flip-chip package with solder bumps and copper pillars

• Main Authors: Wakeel, Saif, Haseeb, A. S. Md. Abdul, Hoon, Khoo Ly, Amalina, Muhammad Afifi
• Format: Article
• Published: IEEE-Inst Electrical Electronics Engineers Inc 2022
• Subjects: TS Manufactures
• Online Access: http://eprints.um.edu.my/41404/

In this work, two commercial no clean fluxes, namely, extremely low residue no-clean flux (NCF) (NC-1) and ordinary NCF (NC-2), were used for the preparation of a fine pitch flip-chip package with a 7.6 x 7.6 mm(2) Si die on a 17 x 17 mm(2) organic substrate. One water-soluble (WS) flux was also used for comparison. Moisture sensitivity of the package was evaluated using JESD22-A113D (30 degrees C/60% relative humidity (RH), 192 h, 3x reflow at 260 degrees C). Thermal cycling tests were performed following JESD22-A104D (-65 degrees C to 150 degrees C). The high-temperature storage life (HTSL) of the packages was investigated using JESD22-A103C (175 degrees C). Underfill delamination or voids in the package were investigated by confocal scanning acoustic microscopy (C-SAM). Failure characteristics of the packages were also studied using scanning electron microscopy (SEM). After moisture sensitivity level (MSL) test, vehicles prepared by NC-1 and NC-2 showed failure. SEM images revealed severe delamination between underfill and solder mask in the presence of amine/amide and carboxylic acid-based NCF residue. Solder bump crack were found at <500 cycles for samples prepared with NC-1 which contains tertiary amine and long carbon chain (C8:C10:C12) carboxylic acid-based. However, failure occurred at <1500 cycles for NC-2 containing secondary amide and shorter carbon chain length (C3) carboxylic acid. Samples prepared using WS did not show any failure for up to 2000 cycles. Thus, NCF-treated assemblies performed poorly in moisture sensitivity and temperature cycling tests.