Mechanical Modelling of High Power Lateral IGBT for LED Driver Applications

Abstract

Abstract-An assembly exercise was proposed to replace the vertical MOSFET by lateral IGBTs (LIGBT) for LED driver systems which can provide significant advantages in terms of size reduction (LIGBTs are ten times smaller than vertical MOSFETs) and lower component count. A 6 circle, 5V gate, 800 V LIGBT device with dimension of 818μm x 672μm with deposited solder balls that has a radius of around 75μm was selected in this assembly exercise. The driver system uses chip on board (COB) technique to create a compact driver system which can fit into a GU10 bulb housing. The challenging aspect of the LIGBT package in high voltage application is underfill dielectric breakdown and solder fatigue failure. In order to predict the extreme electric field values of the underfill, an electrostatic finite element analysis was undertaken on the LIGBT package structure for various underfill permittivity values. From the electro static finite element analysis, the maximum electric field in the underfill was estimated as 38 V/μm. Five commercial underfills were selected for investigating the trade-off in materials properties that mitigate underfill electrical breakdown and solder joint fatigue failure. These selected underfills have dielectric breakdown higher than the predicted value from electrostatic analysis. The thermomechanical finite element analysis were undertaken for solder bump reliability for all the underfill materials. The underfill which can enhance the solder reliability was chosen as prime candidate.

State of the Art of Lead-Free Solder Joint Reliability

“…The accumulated inelastic strain contours at the third cycle in the solder joints are shown in Fig. 43 [113]. It can be seen that the maximum magnitude occurs at the corner solder joint with the largest DNP.…”

“…In 2017, based on his own creep curves data of Au20Sn, Jin [100] determined the nine constants of the Anand constitutive equation, which are also shown in Table 7. Figure 42 shows a high-power lateral insulated-gate bipolar transistor for light-emitting diode (LED) applications proposed by Bailey et al [113]. It can be seen that for the vertical device, the low-voltage terminals are placed on the front side of the die while the high voltage terminal (800 V) is placed on the opposite side of the die.…”

“…The temperature boundary conditions are ramp time ¼ 3 min and dwell time ¼ 15 min, and À25 ! 125 C. The SOLID185 of ANSYS has been used [113]. The constitutive equation of the Sn3.5Ag solder is given by Wang et al [102], Table 7.…”