I am currently working on a project where we are trying to limit costs as much as possible and one of the results of this is trying to avoid using IMS(insulated metal substrate, in this case 0.125" aluminum instead of the typical FR4 in PCBs) in the power board design. We currently use an IMS in a large portion of our designs, however this particular job is more competitive and we are hoping to avoid the cost and slower procurement of the IMS.
The basic setup of the power board is a charge FET(s) and a discharge FET(s) as shown in the basic schematic below. There is a fair bit of control circuitry for the FETs that is not shown, as it is both complex and proprietary, and shouldn't be relevant for the scope of this question.
For this project the current requirements are 120A charge for 3 min, followed by 4A discharge for 90 min, and repeated continuously for the life of the battery. The FETs we are planning on using are IPT015N.
The current design idea I am working with is a stamped copper bus bar with rounded square protrusions that fit in a slot in the FR4 allowing the drain tabs of the FETs to be soldered directly to the bar. This has the benefit of allowing us to put both control and power circuitry on the same board, as well as being much easier to have manufactured and prototyped.
Is this bus bar protrusion a reasonable approach to draw heat from the FETs in large-scale production? While the testing indicates it is a viable option, it seems to be rather unique approach.
Are there any other alternatives to IMS that are cheaper and could be effective in this scenario?