Functionality and Examples of System-on-Modules

Systems of Modules (SOM) offer a unique approach to product development and the often fully customized electronic devices often included in complex devices.SOMs enable system designers to implement fully customized electronic components, including custom interfaces and form factors, without having to design electronics from scratch. Customers can purchase an off-the-shelf SOM and combine it with a custom substrate that is easy to develop. 
SoMs are typically built on top of the PCB and can either be encapsulated in a metal enclosure (EMC compliant) or exposed and display all components. In addition, SoMs always have a way to connect to external boards in the form of pins, edge connectors or solder tabs.

Functionality of System-on-Modules

SoMs are not as common as SoCs, but their role will become increasingly important as semiconductors approach their physical limits, SoCs are chips that integrate multiple system components into a single device. However, SoCs still require external circuitry to enable the device to operate, which may include memory, I/O controllers, and various other supporting components. 
As a result, using SoCs in a design can make the design process complex and tedious. Designers need to fully understand how to properly use SoCs, including the function of each pin, the thermal characteristics of the SoC, and the pad design. However, SoM creates a module to handle these complexities to produce a device that designers can essentially put into a circuit. 
Like Arduino, the SoM's pins can be connected directly to any hardware the designer wants to use. However, if the Arduino is a prototyping platform, the SoM can be used for a final product with a high degree of reliability.
Another major advantage of using SoMs is interchangeability. Assuming the manufacturer of the SoM maintains the module form factor, technical improvements can be incorporated into newer SoMs that can be easily interchanged with older units. As a result, expensive and complex systems can be upgraded without completely changing the underlying hardware.

System on Module examples

If we define SoM as a device that allows the use of multiple system functions in the final product and combines them into a single PCB, the answer is that system-level modules are very common in the industry.
One of the electronic areas where SoM is heavily used is radio communications, especially in the 2.4 GHz band. the ESP32-WROOM-32 is an example of an SoM that integrates a microcontroller, TCP/IP stack, radio circuitry, radio antenna and memory all into a single PCB with a metal enclosure. While some versions of the module are attached to a board with pins for prototyping, the module itself can be purchased and soldered directly to a PCB in the final product, operating as a Wi-Fi adapter or as a sole controller.

The SOM approach has many benefits over developing from scratch. These include cost savings, risk reduction, multiple CPU options, reduced customer design requirements, small footprint, and significant time savings because software developers can use off-the-shelf hardware with the same processing core as the finished product.