What's wrong paralleling schottky diodes?

[Kokoriantz]

I need low voltage drop SMD diodes for 300khz PWM with 5.5Ap current for low loss flywheel and low dissipation running with 48V.
I did find from ST micro 5A60V for $0.5 that has 0.55V but I wonder if 5.5A at 95%PWM at 20Hz is acceptable.
On the other hand, there is the very cheap SS510, I ordered 50pcs for $1.2. As the project is intended for DIY use only, I can ask the 3 paralleled diodes to be matched which also helps the heat to be scattered.

[moffy]

The negative temperature coefficient of diodes means that the one carrying the most current will heat more and carry more current etc. They need to be matched and thermally bonded together to prevent a single diode hogging the current.

[CosteC]

I would parallel diodes in the same package - there is lot of dual diodes.
Single devices - rather not. Testing and pairing is something I try to avoid.
SK86C from Taiwan Semiconductor?
PDS760-13 from Diodes inc?

[Kokoriantz]

Although both references are single diodes, the pds760 is a better choice than 50l60 and cheaper from Ali, $3 for 10pcs all Inc.
I will run it hot so that at 4A, as I reduced to, it drops only 0.4V dissipating for a pair 1.6W and 3.2W for the 4 units in bridge.
This solved my problem, thank you very much.

[David Hess]

Paralleling diodes can work however their negative temperature coefficient and differences in voltage drop and mean that they will not share current evenly.  To help with this, mount the diodes in close proximity and match their forward voltage drops at a current close to their operating current.

It is possible to calculate a derating factor based on thermal coupling between the diodes and differences in forward voltage drop, however somewhere between 60% and 80% is typical.

As the project is intended for DIY use only, I can ask the 3 paralleled diodes to be matched which also helps the heat to be scattered.

It does help, but unfortunately the requirement to maximize thermal coupling conflicts with this.  I would mount them as closely as possible to each other and rely on derating so there is still some benefit.