Wenjing Zhang

Electroless plating copper cones on leadframe to improve the adhesion with epoxy molding compound

A simple method to increase the adhesion strength between leadframe and epoxy molding compound (EMC) was reported in this paper. Cone-structured copper film was deposited on copper-based leadframe sheets by electroless plating. SEM observation of the as-prepared film indicates that cone size distinctly depends on plating time. Adhesion strength between EMC and cone-coated leadframe was measured by button shear test (BST). Results show that when deposition time t≤120s, the adhesion strength increases rapidly with the growth of copper cones, when t >120s, although cones keep growing, the adhesion strength tends to level off. Average adhesion strength reaches maximum value of 33.80(±1.74) MPa, increased by 87% (57%~124%) when substrate was plated for 600s, compared with that of conventional leadframe. By observing leadframe side of fracture surface after destructive button shear test, two failure modes were proposed: failure at interface and inside EMC. It is assumed that the copper nano-cones structure could effectively increase the contact area of EMC and leadframe, which leads to mechanical interlocking. Such micro-nano structure and its unique property are expected to be applied in the practical industry.

Sample preparation device for molding compound adhesion test

Moisture ingression in plastic packages generally occurs through delaminated interfaces between different materials. So the adhesion strength between molding compound and substrate is crucial to the plastic package reliability. In the present work, a sample preparation device was designed for molding compound adhesion test. A series of experiments has been done with this device. The results showed that the data obtained with this device was stable. The data fluctuation was relatively small. The sample preparation device was effective in molding compound adhesion test.

Solid-state bonding using metallic cone layer for interconnection

This paper describes the feasibility of using metallic cone layer in solid-state bonding with Sn-based solder. At temperature below the melting point of Sn, both Ni cones and Cu cones were found successful in forming robust joints with good bonding strength and compact interfaces. This method is also compatible with high-density micro bump interconnecting. Studies have also been carried out in combination with surface activation bonding. Mechanical insertion and controllable interfacial reactions functioning as key factors for realization of the bonding method were emphasized through theoretical study. This bonding method is expected to be potential for the applications in 3D integration.

Study on the adhesion and reliability of Epoxy Molding Compound and shaped Pd Preplated leadframes

The weak adhesion between the Epoxy Molding Compound (EMC) and Pd Preplated leadframes (Pd PPFs) often causes delaminations and reduces the reliability of integrated circuit. This paper reports on a practical method of dramatically improving the adhesion of EMC and Pd PPFs using electroplating shaped nickel layers. Button shear tests indicate that the adhesions between the EMC and three different shaped nickel PPFs is 169% higher than that of conventional PPFs. The reliability of the adhesion improvement effects was detected by Moisture Sensitivity Level l(MSL-l) test and high temperature button shear test, which proved the high reliability of the shaped PPFs. The mechanical interlocking effects caused by increased surface roughness are the major reason for the improved adhesion as well as the transition of failure modes from adhesive failure to cohesive failure.

Preparation of pine-like Cu-Ni-P coating and its application in 3D integration

A hierarchically structured Cu-Ni-P film fabricated via one-step route of electroless plating is reported. The morphology of deposits can be controlled by adjusting the additive in electrolyte. Due to the synergistic crystalline modification of polyethylene glycol (PEG), Janus Green B (JGB) and Cl−, the as-prepared Cu-Ni-P film exhibits pine-like architecture, about 2 µm in height and 1.5µm in root diameter. EDX result reveals that the pine-like coating is composed of about 94% Cu, 5%Ni and 1% P (weight %). Combined with the results of Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM), it can be seen that the pine-like Cu-Ni-P structure is ploy-crystalline. Bonding test shows that the adhesion strength between Sn and pine-like Cu-Ni-P substrate is about 8.4MPa. The reason for the excellent bonding performance could be ascribed to the mechanical interlocking effect caused by the roughened surface, which is proved to be an effective way to achieve low temperature bonding of Sn and Cu.

Electroless deposition of copper alloy in the PEG additive

In this paper, Cu alloy with rough micro-scale morphology was successfully electroless plated with the help of polyethylene glycol (PEG) additive. The morphology was observed by SEM and electrochemical mechanism of micro-nano-structured Cu alloy formation was analyzed using linear sweep voltammetry. Results show that increase in PEG concentration could inhibit the anodic and cathodic reaction and the growth of secondary structure on the cone surface. The different type of crystallization modifier could result in different surface morphology. And the adsorption effect of PEG increases with the molecular weight.