Search

In this paper, authors developed miniaturizeddouble side cooling packaging for SiC (silicon carbide) highpower inverter module using new material solutions towithstand high temperature condition over 220oC. Instead ofconventional thick wire bonding on the device, the flip chipbonding for high power source and gate interconnections aredeveloped. For the drain interconnection, copper clips areattached using high temperature endurable interconnectionmaterials. By utilizing these flip-chip structures, the powermodule with double side cooling design was enabled effectivelyfor the heat dissipation induced by high power switchingoperation. Through the thermal modeling and characterization, the power module's package thermal dissipation performancewas found to be enhanced by 2 times compared with theconventional single side cooling type power module. To copewith the increased maximum junction temperature limit tooperate wide band gap power devices the novel packagingmaterial and its process which can endure up to 220 oC weredeveloped also. Bi and Ag based high temperature solder wasapplied for the flip-chip bumping for SiC device on the DBC(direct bonded copper). The copper clip was applied on thedevice backside as drain interconnection to DBC also. Hightemperature endurable EMC (epoxy molding compound) andTIM (thermal interface material) were also evaluated. Thepackaging process was optimized and developed along with themodeling. Through the reliability assessment, we could showthe potential applicability of double side cooling power modulewith flip-chip and clip bonding design and it would be usefulfor the SiC and GaN based high power module and highjunction and environmental temperature endurableapplications for the near future.

Ag sintering has been widely studied as a lead-free die attach solution for power electronics. A soak time of a dozen minutes at the sintering temperature is necessary to establish strong bond strength by the conventional heating method. Chemical bonding can be achieved by various parameters associated with the metallurgical bond of the adjacent surfaces. In this study, attaching technology between Au coated Si die and Au coated Si substrate was developed by applying Ag sintering materials which can work at temperature up to 350°C. It was concentrated on finding so called "pressure-less sintering and pressure sintering" procedure in air and N2 environment. The sintering was performed in air or N2 at temperature range from 180°C to 280°C for 10 minutes to 3 hours. Highest shear strength was obtained at 200°C of sintering temperature bonded for 3 hours.

While leadframe has come a long way as a cost effective substrate, there is still limitation over its design rule. In this article, the authors have developed and put to test a SiC based PQFN using 70μm single metal layer substrates, allowing further miniaturization and complex design of PQFN. New high temperature EMC with a Tg of 241°C and lead free bismuth silver solder are adopted. Reliability tests and RDS,on results showed that the materials adopted in the development does not degrade the MOSFET's functionality and all samples passed reliability and power cycling tests.

Lead-free solder alloys for high temperature applications is required to meet increasing demands for reliable replacements for lead-based alloys. Especially, high temperature solder is required for bonding in power electronics packages where first bonding on a lead-frame is performed at a temperature of about 330 °C. In this study, the SiC based TO-220 power package was developed by applying high temperature endurable material sets which can endure over 220°C device junction temperature. The interfacial reaction and reliability of SiC die attachment on and Ni plated lead frames using Zn-Al based solder was investigated. Zn-Al-Ge solder alloy showed good temperature tolerance after temperature cycle (TC), high temperature storage test whereas Zn-Al-Ge-Mg solder alloy showed failures after TC test.

There are five types of die attach materials with high melting point (>250°C) are evaluated in this study, these materials are high lead (Pb95.5Sn2Ag2.5) solder paste, Gold Tin (Au80Sn20) solder paste, pressure-less Silver (Ag) sintered paste, pressure type silver (P-Ag) sintered paste and Gold Germanium (Au88Ge12) perform solder. The reliability tests included high temperature storage (HTS) at 250°C/500hours with N2 purge and temperature cycling for 500cycles at −65°C to 150°C. Majorities of the test vehicles have good shear mode (Silicon die crack) after reliability tests. Only mix modes failure on the pressure-less Ag sintered die attach materials is observed at HTS 250°C, after 500hours with shear strength of 17.9Mpa. It is crucial to understand the conditions of the interfaces between these high temperature die attach materials to the devices and substrate after reliability tests. The cross sections samples are further studied on the interface between the die attach material and substrate (ENEPIG surface) with SEM and EDX analysis. It is interesting to found out that the pressure type Ag sintered has denser bulk materials compare to pressure type Ag sintered materials, and this provides an excellent heat transfer and low electrical resistance at the interface. After HTS for 500hours, the Sn rich phase of AuSn solder has the tendency to form at the ENEPIG site. High lead solder form a layer of Ni/Pb/Sn at the ENEPIG surface and where AuGe solder form a layer of Ni/Ge at the interface to ENEPIG substrate. A details study on the materials interface to the die and ENEPIG substrate surface are carried out; and out of these high temperature die attach materials, which will be more preferable in term of process ability and price is discussed.

For downhole drilling applications, packages will have to endure extremely harsh conditions, which can easily reach a temperature of 300°C. At such high temperatures, the commonly adopted solder materials are lead-based as they are more readily available in paste and solder ball forms. While multiple studies have been performed on eutectic goldgermanium solder and its reliability at high temperature, little work has been done on the processing and assembly of the material into a flip chip package. This paper aims to study the feasibility of gold-germanium solder assembly through laser jetting process optimization. It is observed that Ge phase coarsening does not occur with laser jetting, compare to reflow process.