**4. Conclusion**

keep high thermal conductivity throughout the entire product life. In some cases, the joint has degraded thermal conductivity due to the thermal fatigue crack within the joint especially in hot and cycling atmosphere. Therefore, in developing the Alconano®, Nihon Superior has compared the performance of Alconano® versus the high Pb solder and conventional SAC solder after exposure to thermal cycling reliability testing, −40°C/+200°C with dwell time of

Pb-free liquid-phase diffusion bonding (LPDB) material is another emerging material, which can potentially be used as high-temperature Pb-free die attach material. The bonding process of this LPDB is very similar to the modified BiAg paste mentioned above. Similar to the modified BiAg paste, the LPDB paste consists of two types of powder, high melting point and low

**Figure 12.** Change in thermal resistance of high temperature die attach material in a function of thermal cycling. 10×10

substrate with Cu plate heat sink was used as test vehicle. The sintering condition was 300°C,

mm silicon die on Al<sup>2</sup>

O3

40MPa pressure assisted and 3 min sintering duration.

30 min. The comparison results are shown in **Figure 12**.

106 Recent Progress in Soldering Materials

**Figure 11.** Porosity check after pressurized sintering on Ag sintering joint.

Due to RoHS compliance, electronic industries have stopped adopting the stable and familiar SnPb-6337 solder, which was used as electrical interconnect for decades and migrated to Pb-free solder. There are many developments of Pb-free solder with the objective to fulfill the manufacturability and reliability expectation from the users. This kind of development has flooded the market with many alloy compositions and increased the difficulty for user to select a right Pb-free alloy, which can meet their expectations. Since 2006, generally, there are three generations of Pb-free solder being introduced into market. The first generation of Pb-free solder is the conventional SAC alloy with high Ag bearing ranging from 3.0 to 4.0%. Then, the market is moving into low SAC alloy due to the surge of Ag price in early 2010s and the poor drop impact resistance of these conventional SAC alloys. Recently, due to the aggressive growth of auto electronics and avionics, a new set of requirement in term of solder joint reliability is defined against the Pb-free solder. This is the third generation of Pb-free alloy, which is an alloy system catering for long thermal fatigue life and robust in drop impact resistance. On the other hand, there are still many IC and electronic components still adopting high Pb solder (soft solder) as die attach material. The industries are actively looking for Pb-free alternatives to replace it. Alloy systems such as AuSn, BiAg, ZnAl, Ag sintering material, and LPDB material are the potential candidates on the list.
