Die Bonding of Si/Ni/In with Cu/Ag Lead Frame

Recently, LED (Light Emitting Diode) has made a big progress. Like other electronic device, high power device have led to a movement towards LED. Because LED chip is sensitive to the temperature, thermal dissipation becomes the most important challenge to solve now. In LED package, die bonding is a key point of thermal dissipation. Nowadays, silver paste, soldering, and tin-gold eutectic bonding are usually used in LED die bonding, but these methods have some problems. This research provides a new die bonding method which called solid liquid inter-diffusion bonding (SLID). In this procedure silicon wafers (sputtering nickel and indium) assemble copper lead frames (sputtering silver) and silver substrate at low temperature to make indium and silver turn to intermetallic compound. This research also studies the die shear force at different bonding temperature and different bonding time.
The result is as follows, in silver-indium SLID process, the thickness of silver on copper lead frame must be twice thicker than the thickness of indium on silicon wafer. Thus, we can make sure the reaction is complete. In interface reaction, silver and indium will form AgIn2 rapidly at lower bonding temperature. At higher bonding temperature and longer bonding time, besides Ag2In which is the main phase, indium will keep diffusing in silver substrate to form Ag3In. This reaction is complicate, so the N number of reaction kinetics is cast to neither diffusion control nor interface control. By the way, at nickel-indium interface, it will form Ni2In3 intermetallic compound at higher bonding temperature and longer bonding time.
In shear force test, the joint formed at 200℃ and 10 minutes is too weak because AgIn2 exist at this bonding condition. As the bonding temperature increasing, the voids and cracks decrease at the reaction interface. This makes the joint become stronger. If the bonding time too long, the intermetallic compound become too thick. It makes the joint become weaker instead.