The Research On Sn Based Bonding Solder And Process For LED Flip Chip

In this thesis,uses Sn based low temperature solder to achieve bonding of the LED flip chip and the silicon substrate.On the basis of the Sn-9Zn solder alloy accomplish chip bonding and bonding process parameters optimization, and different mass fraction of Bi is added to the base alloy, further reduce the bonding temperature, aimed at bonding chip with the substrate at low temperature approximately at 200~210 ℃.Analyze the bonding failure mechanism and reliability of the bonding,assist with the software such as ANSYS, ImageJ to analysis the bonding structure and quality of the sample, receive theoretical results, analyze and compare with the experimental results.Sn-9Zn solder bonding process research results show that bonding quality improves with the increase of pressure, as the stress reaches a certain level, the stress has a little impact on bonding quality; the bonding quality improves as time increases, when bonding heat preservation time is long enough, time has smaller influence on bonding quality; influence of gas medium on bonding quality is also significant, the condition of formic acid and vacuum are able to get a better bonding quality, among them, under the condition of vacuum than under the condition of formic acid, the bonding shear strength is slightly better. Experiment eventually determine the bonding process parameters are: bonding temperature is 220℃, bonding pressure is 1.5 MPa, the heat preservation time is 20 min, the atmosphere is formic acid.Sn-Zn-Bi solder bonding process research results show that join of Bi elements will reduce the melting point of solder alloy, but adding excessive Bi can lead to solder alloy embrittlement, which affect the bonding quality of the sample. When bonding temperature is 210 ℃, Solder alloy composition of Sn-9Zn-4Bi get the optimal shear strength; when bonding temperature down to 200 ℃, no matter the mass fraction of Bi element, Samples cannot be effectively bonded.Experiments prove that adding nano-silver can reduce bonding temperature of Sn-Cu alloy solder, under the condition of 200 ℃ we can get better shear quality samples. The X-ray detection results of Sn-Zn solder and Sn-Zn-Bi solder bonding sample show that morphology is homogeneous in bonded area, there is no obvious holes, cracks or other defects. After bonding samples present sandwiches sandwich structure, the middle is Cu3 Sn, upper and lower layers are Cu, the shear fracture occurred in the middle layer of the sample, solder alloy occurred certain plastic deformation.