**5. Packaging trend of HEV/EV power module**

The standard of power module for passenger car is stringent than industrial and CAV (Commercial, construction, and agricultural vehicles) products. Therefore, the advanced packaging structure, material, and technology must be investigated.

## **5.1. Novel structures in automotive module packaging**

interconnection to form power inverters, so the pressure must be controlled to ensure the press contact between all package units and cold plates for double-sided cooling. However, the assembly complexity of electrical interconnections is difficult and costly at inverter-level

The Semikron double-sided planar power module using SkiN technology is shown in **Figure 23**. The die top connection is a flex circuit board, and all the joining interfaces between two sides of die and substrate, and DBC and heat sink, are bonded by Ag-sintering process. This provides very high thermal and power cycling reliability, as well as good thermal and

The standard of power module for passenger car is stringent than industrial and CAV (Commercial, construction, and agricultural vehicles) products. Therefore, the advanced

**Figure 22.** Delphi planar bond power module with dual-side cooling [36].

**Figure 23.** Schematic of cross-sectional view of Semikron SKiN power module [43].

packaging structure, material, and technology must be investigated.

**5. Packaging trend of HEV/EV power module**

electrical performance [43].

packaging.

40 Modeling and Simulation for Electric Vehicle Applications

As mentioned above, the direct liquid cooling power module is becoming a standard solution to HEV/EV power packaging. The power density is improved as its excellent thermal per‐ formance and compact integration with heat sink, which is also the volume and weight. *T*<sup>j</sup> max can be well controlled by reduction significantly of *R*th j-h, so the reliability and lifetime are enhanced. By using the advanced cooling structures into module baseplate such as the twophase change flat pipe, vapor chamber and microchamber, etc., the heat transfer efficiency, volume, and weight are further improved.

The baseplate-free module has the advantages in volume, weight, and cost, which is preferred by automotive customers. However, the module with direct substrate cooling structures is more attractive for cooling efficiency, thermal performance together with the benefits of baseplate-free module.

The planar structure is a more advanced packaging trend for automotive module, a top isolation substrate, a flexible PCB or contacting leads are bonded to chip-top contact areas. The bonding wires are eliminated resulting in series benefits in parasitics reduction, temperature uniformity, and reliability. Therefore, the power density, thermal performance, reliability, volume, and weight are improved. By using a top substrate, the module can be cooled from both sides of a chip, increasing the cooling efficiency by more than 30% of a traditional oneside cooling structure.

#### **5.2. Advanced materials for automotive module packaging**

The selection of advanced packaging materials is essential to module performance and reliability, the advanced materials for power semiconductor die, substrate, baseplate, inter‐ connection, and housing are proposed for automotive power packaging.

SiC devices such as MOSFET and Schottky Barrier Diode (SBD) are becoming popular in automotive power module market as its excellent material performance in electrical and thermal. The high bandgap makes SiC devices competent to high-temperature, high-voltage, and high-efficiency applications. Its thermal conductivity is about three times than Si, which is beneficial to high-temperature and high-power density requirements. The doubled electron saturation speed in SiC leads it as best candidate to high-frequency applications. In addition, the GaN devices are developed quickly for automotive product as the same reasons of SiC devices.

Si3N4 substrate is proposed for high performance and reliability power module packaging as its trade-off advantages of CTE, thermal, and mechanical performance. Although Si3N4 is not selected widely at the moment, the reduction of cost in the near future will make it a first choice in automotive module packaging.

AlSiC baseplate with direct liquid cooling pin-fin structure has been extensively proposed in passenger car and sport-racing cars. The reasons also lie in its overall performance advantages of CTE match with semiconductor and substrate materials, good thermal and mechanical features, and lightweight, etc. The advanced interconnection materials such as lead-free solder and copper bonding wire are developed for enhancing reliability and lifetime of automotive module.

The new housing materials are applied in injection molding, transfer molding, and hematic supply high temperature and high mechanical reliability, which are becoming the mainstream housing of automotive module.

### **5.3. The trend of assembly technology**

The assembly technology is essential to power module performance and reliability, so advanced joining and interconnection technologies are being developed for automotive packaging. The trends of joining interfaces between die, substrate, and baseplate are high and stable tensile strength solder layer formed by SnSb, high temperature and reliability interme‐ tallic solder layer formed by transient liquid phase sintering (TPLS), or superior silver-sintered layer. SnSb soldering is an easy and cost-effective way by traditional process; however, TPLS and silver sintering have more reliability benefits.

The conventional Al wire bonding interconnection technique will be replaced by copper wire bonding and planar contacts such as direct lead and flexible PCB bonding. Copper wire bonding improves current and thermal capability, and the reliability, which the planar packaging results in high current, low parasitics, low loss, uniform temperature, and high reliability.

The interconnection of bus bar and pin is usually soldered to substrate in an industrial power module, which have low thermal and mechanical reliability. Recently, ultrasonic welding, which results in quite high bonding strength and pressure contact, is proposed in automotive power packaging. Both enhance thermal and mechanical reliability significantly by eliminat‐ ing interface layers.
