Study on the low-void-ratio vacuum eutectic technology for the Al2O3 ceramic circuit substrate

In microwave power amplifier module, Al
2
O
3
ceramic substrate is a potential candidate for microwave circuit layout, owing to its light weight, low dielectric constant, good CTE for GaN chip, etc. Large voids combined with high void rate are induced in the manual welding process of ceramic circuit substrates. Consequently, various kinds of impedance along with heat and electric resistance could be formed in the microwave power amplifier module. Then it will demonstrate significant impact on impedance match, insertion loss and additional capacitance, and eventually reducing the transmission efficiency of power amplifier transmission circuit. In this contribution, heating curve, the ratio of welder sheet size/ceramic circuit substrate size and the welding pressure were studied in orthogonal experiment configuration. GaN power amplifier module has been packaged with Al
2
O
3
ceramic circuit substrate by Au
88
Ge
12
solder vacuum eutectic technology. Void ratio of the ceramic circuit substrate, solder aspect and shear force were identified by the X-Ray inspection system, ultra-field deep microscope (UFDM) and push and pull force tester (PPFT), respectively. The void ratio of ceramic circuit substrate is less than 5% (the standard GJB548B-2005 requires less than 20%). It can be found the solder is uniformly overflowed via UFDM picture. It is found that the shear force per unit area is higher than 112.3 N/mm
²
, which is about 18 times compared to the GJB548B-2005 requirements (6.25N/mm
²
). Vacuum eutectic technology had the vacuum and inactive gas protect the welding environment, which can form super low-void-ratio welding layer and better Au-Au bonding alloy interface. It can decrease heat and electric resistance for GaN power amplifier module. Ultimately, we can increase the transmission efficiency of power amplifier transmission circuit.