The evolution of electronic products is shifting rapidly. Advanced multi-media products, which are compact and intelligent, are now becoming more familiar in every day life. The demand for portable electronics has also increased the need for small size components with high mounting density. Stacked CSP is the outcome of market demand for greater compactness and lighter weight in cellular telephones, PDAs, digital cameras, and audio players.
What is Stacked CSP? In order to meet the need for rapidly growing applications in the communication and IA markets, ChipMOS has developed the manufacturing technology for stacked CSP, using mini-BGA as the packaging vehicle. The package, with a face-up structure on single-sided circuited BT organic substrate, was developed using wire bonding and transfer molding technology. The dimension of this stacked package could be various with a maximum thickness of 1.4 mm. The external connection terminals are an area array layout of 0.45 mm solder balls with 0.8 mm pitch.
For manufacturing of the stacked CSP, the most important process is the wafer grinding which requires the wafer to be as thin as possible. ChipMOS has achieved the processing technology needed to grind the wafer down to about 100 micro-meter to facilitate the stacking up to 3 chips within the above-mentioned package thickness. To fulfill the thickness limitation, gold wire loop has been kept as low as possible by the use of various bonding methods. The molding system has been modified to comply with the warping substrate. In addition, the sweeping wire and trapped void have been avoided with the help of analysis using the in-house "InPack" 3D simulation software.
Benefits of Stacked CSP Stacked CSP offers several benefits, including :
‧Smaller and thinner packages - More silicon/function per package area - Significant size and weight reduction
‧Reduced packaging costs and component numbers - Include two or more chips in one package, decreasing the number of components - Reduce assembly and test costs - Use conventional materials and manufacturing processes