When embarking on a new RF or microwave design, the cost trade-offs between standard and custom MMICs may not always be as straightforward as one may think. There are several scenarios when can it make sense for an engineer to consider using a custom designed MMIC rather than standard off-the-shelf parts.
Why would anyone try to develop their own custom MMICs when virtually all of the building blocks required in a microwave system are already available commercially? First of all, obviously if the full required functionality doesn’t happen to be available in a COTS (Commercial Off The Shelf) part, then a custom designed MMIC could be the best approach. Likewise if the performance of the available standard product parts falls short of requirements on some parameter, then the custom approach may be preferable to compromising on the final product performance. In some cases this could even involve a non-core parameter, which would not be a consideration for a standard product but may be critical for a specific application.
Going beyond this, for a complex design it may be possible to combine the functionality of multiple COTS MMICs into a single custom MMIC, and this can provide savings in size, cost and power consumption as well as improving performance. Another scenario where a custom designed MMIC could be the right choice is when an existing part is about to be made obsolete. In this case a pin- or pad-compatible replacement is required to avoid having to re-design of the PCB or module, and a custom MMIC can provide this.
Although we normally think of a custom IC as something that is only considered for very high volume applications, this is not necessarily always the case. Initial prototyping costs can be relatively modest, and there are multi-project IC fabrication options that can make prototype fabrication surprisingly affordable. Obviously the design and evaluation fees depend on the complexity of the IC and the target performance but the required volumes to make this a commercial practical option can be significantly lower than might be envisaged.
Being able to specify the exact function of a custom MMIC can help achieve both performance improvements and significant unit cost savings compared with normal supplier pricing ‑ as long as the volume requirements are sufficient.
Designing a custom MMIC incurs many of the same expenses as commercial suppliers: wafer costs, evaluation and qualification costs, test and packaging costs and design team salaries. However commercial suppliers will also be making a significant expenditure on marketing, advertising, after sales support and the operational cost of selling and distributing their devices to customers. All of this needs to be recouped and will be factored into the component pricing, along with a profit margin. With a custom MMIC these costs can be avoided, and the effective unit cost will be significantly reduced
One particular example where a Plextek RFI designed custom MMIC proved to significantly save money was in the case of a client who was using a simple MMIC on a number of different PCBs they had developed, and that part was to be made obsolete. We identified an alternative process, redesigned the part for manufacture in the same package with the same pin-out. We identified a suitable offshore packaging company who could also look after production test and arranged packaging and test through them. The programme worked very well, and a costly PCB re-design programme was avoided.
Other important issues that should be considered when deciding whether to develop a custom MMIC include production test of the die and/or the packaged parts, management of the supply chain once in production, and the desired level of device qualification. These are all issues we can help our clients to address, but they need to be considered early in the development process.