Morphology and Pull Strength of Sn-Ag(-Co) Solder Joint with Copper Pad

Abstract

In order to clarify the effect of the addition of Co to the Sn-Ag solder, the formation and growth of an intermetallic compound (IMC) at the interface between Sn-Ag(-Co) solders and a Cu pad were investigated, and the joint strength of the solder with a Cu pad was also evaluated by a bump pull test. Binary Sn-3.5mass%Ag solder was used as the basic solder, and Sn-3.5mass%Ag-xCo solders (x = 0.1 mass%, 0.3 mass%, and 0.5 mass%) were specially prepared as Co-added solders. For the reflow process, specimens were heated in a radiation furnace at 523 K for 60 s. For the aging process, some specimens were then heattreated in an oil bath at 423 K for 168 h, 504 h, and 1008 h. The results show that the addition of Co to the Sn-Ag solder strongly affected the formation and growth of the IMC at the interface. The results of the pull test clearly show that all solders had similar pull strengths, regardless of the Co addition, although the IMC morphology at the interface of the Sn-Ag-Co solder was quite different from that of the binary Sn-3.5Ag solder.

Effects of Co Alloying and Size on Solidification and Interfacial Reactions in Sn-57 wt.%Bi-(Co)/Cu Couples

“…However, the g-Cu 6 Sn 5 phase has a porous structure with solder trapped in the voids when a minor amount of Co is added, as shown in Fig. 3b, c. The reaction phase morphologies are similar to those in the Sn-Ag-(Co)/Cu and Sn-Ag-Cu-(Co)/Cu interfacial reactions, 7,9 in which the g-Cu 6 Sn 5 phase also exhibits a porous morphology in Co-containing reaction couples.…”

“…However, the e-Cu 3 Sn phase is not observed in the Sn-57 wt.%Bi-0.05 wt.%Co/Cu and Sn-57 wt.%Bi-0.5 wt.%Co/Cu couples aged at 100°C for 1500 h, as shown in Fig. 8b, c. Fe, Co, Ni, and Zn are regarded as effective elements to suppress the growth of the e-Cu 3 Sn phase, 7,9,[27][28][29] and the results mentioned above are in agreement with the literature. Several studies have discussed the suppression of e-Cu 3 Sn phase growth by minor alloying additions.…”

“…Several studies have discussed the suppression of e-Cu 3 Sn phase growth by minor alloying additions. 7,27,29 However, the reason for this effect is still not very clear. It is likely that the solubilities of minor alloying elements in the reaction layers stabilize the g-Cu 6 Sn 5 phase.…”

“…[1][2][3][4] With the development of Pb-free solders, in addition to the design of new alloys, there has been much recent effort on finetuning of existing solders through minor alloying additions. [5][6][7][8][9][10][11][12] Most such studies are on modifications of the prominent Sn-Ag and Sn-Ag-Cu alloys, and Co has been identified as a very effective element [5][6][7][8][9][10][11] to refine the microstructure and improve mechanical properties. However, there are only a few investigations on minor alloying effects of Sn-Bi-based alloys 12,13 and no previous study regarding the effects of Co addition on Sn-Bi alloys.…”

Estimation Method for Liquidus Temperature of Lead-Free Solder Using Differential Scanning Calorimetry Profiles

“…As a result, great efforts have been made to develop lead-free and environmentally sound interconnect joining technologies as alternatives to Sn-Pb eutectic soldering technologies. [1][2][3][4][5][6][7] The use of lead-free solder such as the Sn-Ag-Cu system and the Sn-Cu system is advancing throughout the world. Considerable research efforts into the characteristics of lead-free solder are underway to improve lead-free solder technologies.…”