Alu bond wire - TOLL MOSFET
Q: It was mentioned that the Cu bondwire can’t be used for TOLL MOSFETs with 300A due to physical limits. What is this limit, while Cu is normally the better thermal conducting material?
A: It was a comparison between Al-bondwire and Cu-clip and not Cu-bondwires
It is true that Copper is a better conductor than Aluminium (almost twice as good), but:
- Thick Al-bondwires cannot be replaced with Cu-bondwires. There is no process for thick Cu-wires (they are too hard) and one must use many thin Cu-bondwires instead of one thick Al-bondwire. Cu-BW could only be used for the Gate-connection.
- For the current in a leadless package, the limiting factor at the Source-connection is not the connection of the chip, but the contact surface to the PCB. For e.g. for a TOLL 40V in SFET4, IPLU300N04S4-R8: the chip itself is capable to conduct 700A, the BW limits the current to 550A and the current density of the Source-contact limits the current to another 300A against Electromigration i.e., use of Cu-clips would probably not help us with the current rating. This is not currently the case with MOSFETs 60V, where the Rdson*A is higher and thus the chips are less current rated.
- Another issue is the package Resistance. Because the technologies are becoming more low-impedance, the influence of the package Resistance on the overall resistance becomes higher. Cu-clip would allow reducing the package resistance compared to Al-BW. It is however a new concept for the TOLL package and it must be examined first. Bonding is currently a very good controlled and robust process that does not cause any additional stress to solder joints, which are additionally vulnerable to voids.
Example Datasheet for IPLU300N04S4-R8 can be found https://www.infineon.com/dgdl/IPLU300N04S4-R8-Data-Sheet-10-Infineon.pdf?fileId=5546d4614755559a0147... here.