DCB Substrate Research Articles

Characterization of solder joints made with VPS on DBC substrate

Ensuring the best quality of the solder joint can be crucial in assemblies which operate in different environmental conditions, since the reliability of the whole circuit depends on the quality of the joint. Solder joints on a ceramic substrate can be more prone to cracking because of the higher stress generated in the metal layer than is the case with simple FR4 substrates. In addition soldering methods like vapour phase soldering or convection soldering can have a significant influence on the solder joint’s mechanical quality because of the thickness of the intermetallic layer, the number of voids, solved intermetallic compound and precipitations in the joint. Solder joints from a SAC305 (96.5 %Sn3 %Ag0.5 %) alloy were prepared on DCB substrates which have Al2O3 as the base material which is covered by a Cu wiring layer and an Ni/Au solder preservative coating. Three different soldering methods were used, vapour phase soldering with and without the vacuum option with convection reflow soldering as a reference. The solder joints were studied by shear strength measurements, 2D and 3D X-Ray computed tomography to evaluate void formation. The fracture surfaces and cross-sections of the joints were studied by optical and scanning electron microscopy to compare the microstructural differences of the joints. The tests carried out showed the particular relationships between the mechanical strength of the solder joints and the applied soldering technology in the case of DCB substrates.

An Experimental Study of High Voltage SiC PiN Diode Modules Designed for 6.5 KV / 1 KA

The paper describes first results of 6.5 kV SiC PiN diode modules which are designed as neutral point valves for medium-voltage power inverters rated for 1000 A. The power module consists of 4 AlN DCB substrates soldered on an AlSiC base plate. Each DCB is equipped with 20 SiC PiN diodes operating in parallel. The total active area of all 80 diode chips is 5.68 cm². At the rated current of 2 x 500A the forward voltage drops from 4.1 V at room temperature to 3.9 V at an averaged junction temperature of 125°C. The switching experiments show a very low reverse recovery charge of about 30 µC only. The conduction loss is comparable to the corresponding 6.5 kV silicon diode whereas the dynamic loss is marginal with respect to the forward conduction loss if the switching frequency is held below 10 kHz.

Effects of metallization thickness of ceramic substrates on the reliability of power assemblies under high temperature cycling

This study focuses on the influence of metallization thickness of ceramic substrates on reliability and lifetime of electronic power assemblies under high temperature cycling. The paper presents experimental and numerical results on different test vehicles with a number of DCB substrates with AlN ceramic and different copper thicknesses. It will be shown the influence of the DCB metallization on failure modes such as ceramic fracture and solder delamination under high temperature cycles. Finally, these samples will be compared with DCB substrates equipped with dimples and DAB substrates. Furthermore, the main factors that could increase the lifetime expectancy of power modules in such harsh environments will be identified.

INVESTIGATION OF THE INTERFACE OF THE DCB SUBSTRATE

DCB means direct copper bonding and denotes a process in which copper and a ceramic material are directly bonded. Between the temperature of the metal's melting point and the eutectic temperature of the metal-oxygen, DCB depends on the eutectic compound to join the copper and the ceramic. We do some research to investigate the interface between the copper foils and Al2O3 ceramics; it is the key factor in influencing the performance of the DCB substrate. We also discuss how to get good microstructure of the DCB interface.

Thermal Resistance and Temperature Cycling Endurance of DCB Substrates

Automotive ignition modules are constructed employing power transistors which are soldered to metallised ceramic substrates to achieve electrical insulation and good heat dissipation. Research activities were aimed to substitute potentially hazardous BeO ceramics by means of DCB substrates using non toxic Al2O3. To fulfill reliability requirements as well as thermal conductivity specifications, the DCB compound has to be optimised with regard to thermal stresses, material properties and interconnection technology. Complementary, appropriate test criteria have been established to characterise the performance of DCB substrates in the ignition module.