Low Cost Flip Chip Packaging Strategy

Based on the looking for the low cost flip-chip solution,by analysis the technology,the investment and the difference of the bonding process and the bump process,I found using the existing equipments and process will be a shortcut.Using the wire bonding process to make the bump will be a best choice for low cost bumping process.The arrayed pads can save the die size and best comports with the flip-chip process.To save the die area and match the requirements of the low cost flip-chip process,the arrayed pads for wire bonding need to be put on the active integrated circuits(POC).To find the reliable POC structure,we make some test chips and evaluated through the bonding process.The height of the top metal layer was added to 1.2um from 0.8um,and an extra metal was added as a buffer layer.The buffer layer was patterned in two structures:the frets structure and the line structure.To avoid the effect of the package process the test chips were packaged in ceramic and plastic type.The test results of the plastic packaged chips were familiar with the ceramic packaged chips.So there is a little effect to the POC structure from the package process.The effect to the POC structure is focused in the bonding process.From the test results,we can find the bonding process can make the Vt and lon low down.But the Vt and lon of the test chips with the added buffer layer can match the spec.And the results of frets structure test chip is better than the line structure test chip.The frets structure is the better choice.All the two kinds of POC structure get through the shear test and the reliability test,the structure,applied a stress buffer layer between the inorganic overcoat and top metal layer,can match our low cost requirements.Wire-bonding bump process and the arrayed POC structure will be the most competitive process for flip-chip.