Drawbacks and disadvantages of insulated metal substrate PCBs

Question

Insulated metal substrate (IMS) PCBs, with variants and names including aluminium base, metal clad printed circuit board (MCPCB) and thermally conductive PCBs have some sought-after features in terms of heat conduction and mechanical stability. What I'm looking for are lesser known drawbacks. To start off, I'd mention the ones I already know:

• Costly.
• In basic configuration only suitable for single sided SMT.
• Even more costly and complex if more than one layer is needed.
• Mechanical disadvantages in some settings including vibrations.
• In basic configuration usually have quite thick copper: 3oz, although thinner copper is possible.

Answer 1

I think you have the major ones listed.

They may be more costly to assemble as well, they weigh more than a standard PCB, and rework can be harder.

You may not be able to use fine pitch devices like some BGA packages depending on the vendor's capabilities. Of course large BGA devices probably wouldn't be routable anyway.

Edit: Bryan mentioned eddy currents in the comment above, that could conceivably be an issue as well for high frequency power conversion or RF circuitry.