An Investigation on AlInGaP Die Crack during LED Die Attach Process

Die crack is a potentially serious issue affecting reliability and performance in Semiconductor industry. As a result, customers, particularly in the automotive industry, are concerned about the consequences of this failure mode and expect zero defect. In view of this an investigation was carried out with a focus to eliminate die crack occurrence in the AlInGaP die used in certain LED packages. Crack are only observed in AlInGaP die, other die such InGaN material system were found not exhibit cracks under similar conditions of design and process. Using a process mapping approach, it was observed that cracks only occur on one particular die attach (DA) equipment model. The lower elastic modulus of GaAs combined with the crystal orientation creates condition where external forces during LED assembly, in particularly in DA process, can exceed the mechanical strength of the die causing cracking. It is known that in situation where a crack does not extend into the epitaxial layer, the die will perform well. This makes it impossible to detect at electrical testing. In a controlled experiment, dice were intentionally subjected to large stresses at DA to induce partial cracks. These LEDs were biased with high current and reverse voltage in cyclic mode to induce further stress and initiate crack propagation. It was found that with further crack propagation, these crack dice we able to be segregated. Combined with correct bond force, which will not mechanically overstress the die during assembly and stress test, shown to eliminate this failure mode in mass production and prevent failure in customer application.