10 factors to consider when looking for an EMS company

Are you not happy with your current electronics manufacturing service (EMS) or PCB assembly provider and want to seek out a new one?  Are you getting ready to launch a new product and your current EMS is not big enough to handle the business?  Have you not worked with an EMS company before and are not sure what to look for in an EMS company?

The 10 biggest factors to consider when investigating a potential EMS company:

  1. The company’s D&B Report
  2. Their certifications.
  3. Number of customers
  4. Age of equipment
  5. Cross-trained employees
  6. ESD policy
  7. Process tracking
  8. Revision control
  9. MRP system
  10. Part verification


1. D&B Report

You can obtain a report on the financial stability of a company by obtaining a Dun & Bradstreet Report (also called a “D&B Report”). The D&B Report will contain a score that indicates the credit worthiness of the company.  A score of 100 is the highest, 0 is the lowest.  The score indicates the likelihood that the company will not miss a payment.

You’ll want to avoid working with EMS companies with poor D&B scores.  Companies with a poor D&B score have the risk of not being able to purchase raw materials and equipment on terms;  they must fully pay in advance with cash – something that they are probably low on.

Not being able to purchase raw materials on terms means they cannot purchase the materials until they have the cash on hand.  This could mean obtaining the parts later than needed, resulting in missed customer shipments.

A low D&B score should be a red flag.  A low score indicates management failure.  A PCB assembly company that is not managed well probably functions poorly in other areas – such as the ability to deliver a quality product.


2. Certifications

In order for an EMS company to obtain certain certifications, an outside auditor or auditors will first visit the company and perform an extensive investigation on the company’s procedures. The company will thoroughly explain to the auditor their operating procedures. These procedures will typically contain some minimum requirements by the certifying authority.

Once the auditor has a good understanding of the company’s procedures, the auditor will then see if the company “practices what it preaches.”  The auditor will pick 1 or more products that the company is currently building and dive into it to see if the procedures were followed as the product was being launched and are still being followed as the product is in production.

When you are considering an PCB assembly or EMS company to work with, you or your QA department may want to perform your own audit of the company.  But this audit of yours could be drastically cut short as a result of the EMS company already passing a 3rd-party audit, as evidenced by their certifications.

It should raise red flags if an EMS company does not have certifications.  You should inquire why.  Did they try to receive a certification but failed?  Maybe they have not tried to become certified because they know that they would fail an audit.  These are troublesome answers.  This should cause you to steer clear of working with an uncertified EMS company.

Two of the most difficult certifications to obtain are:

IATF 16949

ISO 9001

You should work with an EMS company that has 1 or both of these certifications.


3. Number of customers

There are several things to look for here. You will want to make sure your potential PCB assembly / EMS company has a healthy mix of customers – both in number and in industries.

Confirm that the EMS company that you are considering for electronic manufacturing services doesn’t have a very high percentage of their business with just 1 customer.  This is not healthy.  When the EMS company’s big customer goes away, then the EMS company stands to suffer financially.  An EMS company experiencing financial stress runs the risk of having to layoff experienced workers, not being able to pay for raw materials, etc.

Similarly, you’ll want to make sure that most of the EMS company’s business is not with just 1 particular industry.  For example, it would not be a good thing for an EMS company to have 90% of their business with the Defense industry.  If the Defense industry experiences a drastic downturn, the EMS company will experience the same financial problems mentioned previously.


4. Age of equipment

When you visit a potential EMS company and get a factory tour, ask about the various pieces of manufacturing equipment that you see. Is the exact same equipment no longer being made by the machine maker? Is it obsolete?  If so, is the EMS company on some long-term support contract with the machine maker?  How many more years will spare parts remain available?


5. Cross-trained employees

When you visit an EMS company and see programmable equipment – such as SMT machines, solder reflow ovens, functional testers, etc. – ask who programs these machines. You will want to make sure that the knowhow for a given piece of equipment does not reside with a single employee. The reason is obvious: if that person leaves, the company is left with probable downtime and/or quality issues as they try to find a replacement.


6. ESD policy

Electronic circuit boards are extremely susceptible to ESD damage. This may come as a surprise to you. You probably have never damaged with electrostatic discharge your smartphone, your computer, your TV remote, or any number of electronic devices that you use in your everyday life.  You have been able to avoid damaging the electronics you use in your everyday life because the enclosure that the circuit board is in isolates you from the sensitive electronics on the circuit board.

If the circuit board does have an exposed area on the enclosure (such as a charging port or a communication cable connector), the circuitry on the PCB around this exposed area includes some ESD protection circuitry.  Typically, this ESD protection circuitry is placed just in areas (such as around a connector) where a person could physically touch it.

Obviously, in an electronics manufacturing company, humans will touch a circuit board in any possible area – not just where ESD protection circuitry exists.  Therefore, to prevent a board from getting ESD damage, the EMS company must have strict ESD practices.

Ideally, the PCB assembly / EMS company should have an ESD floor.  Such a floor prevents any charge build-up on the production operators – provided the operators are either wearing special ESD shoes, or have ESD straps connected to their shoes.

If the company does not have an ESD floor, the operators must be extremely disciplined to connect their ESD wrist straps to the various grounding connections as they move around the production floor.  This type of discipline is very difficult to maintain perfectly.  All it takes is for an operator to forget to ground herself 1 time to potentially damage boards.

Whether a company uses an ESD floor or uses wrist straps, it is crucial that the EMS company has a policy in place that requires the production operators to test their ESD grounding straps (foot strap or wrist strap) before being allowed on the production floor.  Wrist straps are especially prone to go bad as a result of all the flexing the cable endures.

As you get a tour of an EMS company, point out some operator’s ESD wrist or foot strap and ask how do they know that strap is good?  Be on the lookout for some operator not having a wrist or foot strap.


7. Process tracking

An EMS company will have a variety of printed circuit board assemblies (PCBA) in production. It is very common for these different assemblies to have different processes. For example, one assembly may require CC (conformal coating), while another assembly does not.  Some assemblies require ICT (in-circuit testing), some do not; some require selective soldering, some do not.

With the multitude of different requirements each PCBA may have, it is especially easy for newer/less experienced operators to skip a production step or missroute product.

A good EMS company will heavily rely on barcode scanning.  Such a company will have software in place on the various production machines that require an operator to scan an assembly’s barcode.  The software will then query a process tracking database to make sure that the assembly passed all previous production steps.

When you tour an EMS company, ask to see what happens when a previous production step is accidently skipped or fails.


8. Revision control

It is common for a printed circuit board assembly to go through several revisions during its production lifetime. How does your potential EMS company handle these revisions?

Let’s take an example.  Let’s say you have your EMS company manufacturing circuit boards for you.  After 2 months your engineers want to update the firmware that is flashed on some IC on the circuit board.  You tell your EMS company that you no longer want “rev A” assemblies.  You now want the “rev B” assemblies that have the latest firmware.

The EMS company says that they will no longer ship any “rev A” assemblies.  How can they assure this?  Even if the company scours the production floor and gathers up all the “rev A” assemblies and quarantines them, it still could be possible for a “rev A” assembly to get shipped.

During the gathering up process of all the “rev A” units, it is possible a tote of “rev A” units got overlooked and they remained on the production floor.

An engineer may find a “rev A” assembly in his desk drawer and think, “Oops.  I borrowed this unit off the production floor last month and forgot to take it back.  I’ll return it now.”

A good EMS company will have a process tracking system (previous point) that takes into account a product’s revision.  With this feature, as the product is barcode scanned at various steps on the production floor, when an old revision of an assembly is detected, the production operator is shown an error message, telling him that the unit is from an obsolete revision and cannot be processed.


9. MRP system

MRP stands for material requirements planning. An MRP system is a software system that helps a company plan and schedule production. It also triggers the buyers within an EMS company on what raw materials to purchase and when to receive them by.  An MRP system takes into account various things inputted into it such as:

  • Lead times for components
  • Customer orders
  • Bill of material for each assembly

With the possible exception of the smallest, bootstrapped EMS companies, it is impossible for any EMS to take into account all the variables regarding an assembly and making sure that orders for raw materials are placed at the correct time.  This is the job for the MRP system.

An EMS company that does not use an MRP system is bound to be either sitting on too much inventory or probably missing customer shipments due to lack of raw materials.


10. Part verification

When raw materials are issued from the warehouse to the production floor, how does your potential EMS company know that the correct parts were issued?

When you get a tour of a potential EMS company and you see the SMT operator loading reels of parts, ask your tour guide how they know that reel holds the correct parts.

A good PCB assembly / EMS company will have multiple layers of protection to prevent an assembly from being built with the wrong parts.

The PCB assembly / EMS company should have measures in place that prevents the warehouse from issuing the wrong part to the production floor.  Ideally, this involves the warehouse operators barcode scanning components.

A 2nd layer of protection should exist on the production floor.  Even if the warehouse somehow issued the wrong parts to the production floor, or, if a production operator grabbed the wrong reel/bag of components to use, a system should be in place to alert the production worker that the parts are wrong.  Again, the best protection method would involve barcode scanning.



There are other points to consider when looking to team up with a contract manufacturer of your printed circuit board assemblies.  But if you find one that meets the 10 items above, you could have found a good one.  If the PCB assembly / EMS company does not meet one of these items, you need to continue your search.