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Start with the technology.
      
It is usually simple to identify the technology necessary to assemble a PCB.  There are many types of boards, and types of insertion equipment.  Insure that your potential supplier has the right tooling for your specific needs.  Also inquire about expansion plans as they may affect you in the future.

Choose a size that fits your company.

The biggest PCB assembly companies are often the biggest for good reason, they provide excellent service.  One thing that is rarely talked about are target customer sizes.  Most PCB assembly companies have a specific size of customer they target.  For example, many large assemblers do not want customers that will do less than a few million in annual business with them.  As a company outgrows its current customer base it can raise those limits, leading to "Dear John" letters to some of its customers, even those who have been with them for years.  Establish how much of a company's sales you want to be.  If you are too big, they may depend too much on you, and if you are too small for them, they may not want to service you long term.

Material Cost and buying power.

One of the biggest advantages of a well run PCB assembly company is the way they leverage their buying power.  A good buyer can negotiate preferred pricing for the CM.  If your company already has negotiated prices on specific raw materials, it is helpful to let the supplier know about it.  It is also important to consider proprietary parts and how you want them handled.  You may need a letter to authorize the component manufacturer to release pricing to your supplier.

PCB Assembly companies are varied in ability and focus.  Proper evaluation of these potential suppliers can lead to a long term relationship that is profitable for both companies.

Articles are the opinion of the writers and are not necessarily an endorsement or criticism of any particular supplier or service.