Purpose: The purpose of this paper is to present a failure analysis of the solder layer in a Darlington power transistor in a TO-3 package. Design/methodology/approach: A failed Darlington power transistor in a TO-3 package was examined by different kinds of failure analysis techniques. At first, internal gas analysis was conducted to measure the atmosphere. Then, scanning acoustic microscopy (SAM) was performed to check the quality of the solder layers in the failed device, and the failure location was determined in the solder layer between chip and substrate. Next, the failed device was decapped to observe the defects. After removing the chip from the substrate, energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were applied and the main elemental composition of the solder layer was identified. Findings: Internal gas analysis indicated that the moisture and oxygen contents exceeded the allowed maximum value. Large areas of voids were found in the solder layer by SAM. The main elemental compositions of the solder layer were identified by scanning electron microscopy and EDS. Furthermore, the valences of the chemical components in the solder layer were identified by XPS. Except for the few simple substances of the initial solder material, the chemical formulae of oxidation products in the solder layer were deduced. In addition, the root causes are also discussed. Originality/value: This paper focuses on the solder layer failure of a power transistor. Factors such as the presence of oxygen, voids and other factors, which can cause transistor damage, were comprehensively analyzed. The analysis process is worth learning from and the results can be used to improve the reliability of power devices in this kind of package.

The cementing manufacturing process of ferrite phase shifters has the defect that cementing strength is insufficient and fractures always appear. A detection method of these defects was studied utilizing the multi-sensors Prognostic and Health Management (PHM) theory. Aiming at these process defects, the reasons that lead to defects are analyzed in this paper. In the meanwhile, the key process parameters were determined and Differential Scanning Calorimetry (DSC) tests during the cure process of resin cementing were carried out. At the same time, in order to get data on changing cementing strength, multiple-group cementing process tests of different key process parameters were designed and conducted. A relational model of cementing strength and cure temperature, time and pressure was established, by combining data of DSC and process tests as well as based on the Avrami formula. Through sensitivity analysis for three process parameters, the on-line detection decision criterion and the process parameters which have obvious impact on cementing strength were determined. A PHM system with multiple temperature and pressure sensors was established on this basis, and then, on-line detection, diagnosis and control for ferrite phase shifter cementing process defects were realized. It was verified by subsequent process that the on-line detection system improved the reliability of the ferrite phase shifter cementing process and reduced the incidence of insufficient cementing strength defects.

Long bonding wires may swing significantly and touch with adjacent ones, which will result in short circuit under mechanical condition, especially in aerospace applications. This may seriously affect the operational reliability of high-density hermetic package components. The aim of this paper is to assess the touch risk of high-density package component under mechanical shock condition. An experiment setup, which can obtain the touch critical load and detect the wires swing touch through voltage signal captured by oscilloscope, is designed and built. To obtain the vibration data of different bonding wire structures under different shock loads, numerical simulation models are established after verified by the experimental data. Additionally, initial swing amplitude model, vibration frequency model, and damped coefficient model are established based on the simulation and experiment data. Furthermore, wire swing touch risk assessment model is established in consideration of the distribution of wire structure and shock load deviation. Based on the verified numerical simulation model, vibration characteristic parameters, including the initial swing amplitude, vibration frequency, and damped coefficient, can be calculated by numerical simulation and experimental results. The proposed method can be used to assess bonding wire touch risk in high-density hermetic package quantitatively. Potential touch risk, which cannot be reflected by failure analysis of structure damage after test, can also be detected by the electronic measurement designed in this paper. The proposed method can effectively reflect short circuit between long bonding wires of hermetic package in large shock applications, such as transport and launch.