Chip Bonding Pad Metal Layer Corrosion Problem Research

Plastic semiconductor devices are widely used in various fields, Aluminumcorrosion in the bond pad is a popular issue due to non-hermetic encapsulation features.Poor contact, physical isolation failure, leakage and function deterioration will occurafter bond pad corroded. The purpose of the paper is how to protection againstcorrosion in bond pad.Firstly, the principle of aluminum corrosion was reviewed, and then corrosionsamples were analyzed, after that the phenomena observed in the analysis was verifiedby experiments, and provided solutions.The corrosion in bond pad of aging device can be accurately reappeared byreliability test. The delamination was detected in the samples by Ultrasound scanner,and cross-section analysis proved the existence of it. The corrosion products whichexpand in volume flooded between bond pad and epoxy molding compound (EMC),irregular shape appeared of it in the bond pad were observed by Scanning electronmicroscope and X-ray energy spectrum analyzer detected the main component of it arealuminum, oxygen, silicon and carbon. The roasting corrosion products resultrevealed significantly reduce in oxygen, it prove that it is aluminum hydroxide. Thestudy result shown that the aluminum corrosion reaction was occurred in the bond pad,and corrosion products are aluminum hydroxide.The halogen comes from raw material is not the key factor of corrosion in thiscase because corrosion severity were same even if instead of new material whichcontain higher halogen. Control moisture intrusion is the only way to reduce corrosion.Experiment demonstrated that the delamination issue from thermalstress imbalance of EMC and other materials, and it connected outside and inside thedevice, moisture along the channel reach to bond pad. Optimization of the moldingcompound formula is too costly to popularize. Improved lead frame can besuccessfully prevented delamination, and which is simple and cheap.In addition, experiment result shown that Auto-Clave reliability test is the easy ways to get the corrosion samples, ultrasound scan results can characterize of corrosionseverity, which can save time and increase efficiency.