It seems that most, if not all, companies that produce mass market goods use custom boards rather than putting together modules that are already available in the general market.
For instance, battery chargers use custom circuits rather than some module from aliexpress. Bluetooth speakers also tend to use custom circuits instead of a HC06.
Wouldn't it be more economical to put together existing modules than to build custom boards? Wouldn't that require lower development and testing costs?
Thanks
Best Answer
Another consideration in addition to davidrojas' and the other answers, is that if I as a manufacturer decide to use another commercial product (note: this isn't outsourcing to another company to make my product, but actually purchasing a commercial 'module' as you specify), then I am forever on having to live with it. There are two serious problems there: One, what if the 'Module' has a defect, especially a safety one. Then my company is responsible to bear the brunt of the publicity, and there is no guarantee that I can have the module maker fix the problem, leaving me back at square one, which is designing my own. The second major problem is that the company selling the module to me has no obligation to keep it the same. They can change footprint, connections, features, or even discontinue it at any time.
Major companies that do outsource parts generally still design the parts in-house, and then send them to one or more manufacturers to actually make them. This is true in just about every commercial product from electronics to lawnmowers.