Effects of reflow profile and thermal conditioning on intermetallic compound thickness for SnAgCu soldered joints

Abstract

Purpose -The purpose of this paper is to investigate the effects of reflow time, reflow peak temperature, thermal shock and thermal aging on the intermetallic compound (IMC) thickness for Sn3.0Ag0.5Cu (SAC305) soldered joints. Design/methodology/approach -A four-factor factorial design with three replications is selected in the experiment. The input variables are the peak temperature, the duration of time above solder liquidus temperature (TAL), solder alloy and thermal shock. The peak temperature has three levels, 12, 22 and 328C above solder liquidus temperatures (or 230, 240 and 2508C for SAC305 and 195, 205, and 2158C for SnPb). The TAL has two levels, 30 and 90 s. The thermally shocked test vehicles are subjected to air-to-air thermal shock conditioning from 2 40 to 1258C with 30 min dwell times (or 1 h/ cycle) for 500 cycles. Samples both from the initial time zero and after thermal shock are cross-sectioned. The IMC thickness is measured using scanning electron microscopy. Statistical analyses are conducted to compare the difference in IMC thickness growth between SAC305 solder joints and SnPb solder joints, and the difference in IMC thickness growth between after thermal shock and after thermal aging. Findings -The IMC thickness increases with higher reflow peak temperature and longer time above liquidus. The IMC layer of SAC305 soldered joints is statistically significantly thicker than that of SnPb soldered joints when reflowed at comparable peak temperatures above liquidus and the same time above liquidus. Thermal conditioning leads to a smoother and thicker IMC layer. Thermal shock contributes to IMC growth merely through hightemperature conditioning. The IMC thickness increases in SAC305 soldered joints after thermal shock or thermal aging are generally in agreement with prediction models such as that proposed by Hwang. Research limitations/implications -It is still unknown which thickness of IMC layer could result in damage to the solder. Practical implications -The IMC thickness of all samples is below 3 mm for both SnPb and SAC305 solder joints reflowed at the peak temperature ranging from 12 to 328C above liquidus temperature and at times above liquidus ranging from 30 to 90 s. The IMC thickness is below 4 mm after subjecting to air-to-air thermal shock from 2 40 to 1258C with 30 min dwell time for 500 cycles or thermal aging at 1258C for 250 h. Originality/value -The paper reports experimental results of IMC thickness at different thermal conditions. The application is useful for understanding the thickness growth of the IMC layer at various thermal conditions.

Experimental approach to thermal conductivity of macro solder joints with voids

“…The intermetallic layer thickness changes from 2.60 to 3 μm. The results obtained are typical for SAC 305 (Pan et al , 2009).…”

Effect of Lanthanum Doping on the Microstructure Evolution and Intermetallic Compound (IMC) Growth during Thermal Aging of SAC305 Solder Alloy

“…However, a thick IMCs layer at the solder/conductor metal interface significantly reduces the reliability of the solder joints because of their inherent brittle nature and their tendency to generate structural defects because physical properties (such as elastic modulus and coefficient of thermal expansion) of IMCs are not compatible with parent metal i.e. SAC alloy [1,10,[19][20][21][22][23][24][25][26]. IMC have much higher strength than the bulk solder material [27,28].…”

Analysis of the Interfacial Reaction between Bulk Metallic Glass Coated Copper, Nickel, and Titanium with Lead-Free Solders

“…Studies on the reflow temperature profiles typically focus on the shear strength performance and microstructure characterization. Previous studies reported that the reflowing process had three peaks, 12 °C, 22 °C, and 32 °C above the temperature of the solder liquidus [8]. If the condition has a set excessive peak temperature, then the defect possibilities are delamination, charring, cold joints, excessive intermetallics, leaching, and a brittle solder joint.…”

“…Aging can also lead to the development of an intermetallic compound (IMC). For example, studies reported that the IMC thickness of the SnAgCu connected with solder increased from 1-2.5 to 3-4.5 microns after aging at 150 °C for 300 hours [8].…”