Lately, there’s a lot of companies supplying specialised System On Chip (SOC) solutions for general embedded IoT problems. An IC that’s got a radio physical layer as well as a microcontroller, ram, flash, etc built in, and can be used to create a complete design with minimal external pieces.
Often you end up in the situation where you can either specify the SOC to design your product with, or you can specify a module which includes the SOC and general support circuitry (antenna, matching, power supply decoupling, and sometimes possibly more) This is known as a System On Module (SOM)
The SOC and the SOM do the same thing in your product but:
The SOC design will be cheaper to build each unit at the same production volume. But it requires more design work, and more EMC testing, and sometimes also device qualification depending on the radio technology.
The SOM design means less hardware design needs to happen before a product release. And even more importantly – less testing and verification. It pretty much guarantees a faster time to market, less engineering cost upfront, and less risk to the development timeline. But putting the SOM on your board will take more space than the equivalent SOC layout would, and is not flexible in regards to placement of parts which can cause problems with industrial design and RF performance in wearables. It costs more in ongoing production than the SOC. It can either require headers to attach to your board which also cost money on your BOM and takes up even more space, or be a Pad Grid Array part which is actually quite tricky to solder to your PCB and adds cost to your assembly process.And if it’s a third party product (ie not designed and sold by the SOC manufacturer) you will have to consider ongoing supply and availability.
Depending on the details of your product and the SOM and SOC, it can be obvious where one or the other becomes the winning option. Where it’s not obvious, you have the ability to take the development shortcut for short term product creation, and then go back to a fully custom design at a later date as a manufacturing cost down, once you have sales to pay for the extra work.
For a fast prototyping phase, neither usually matters over the other. You will use an evaluation board for the SOC or an evaluation board for the SOM. And the work to do either will be identical, so you can usually use either evaluation board to evaluate either design option. Unless the SOM is a third party product and provides some combination of extra features or enhanced firmware API.