What happens when a product you produce fails? You customer may call and return the product. They may expect you to provide a replacement or refund.
Does it matter if the failure was due to a capacitor or motor that you didn’t design, just purchased?

No.

Does it matter if a supplier’s supplier made an error that directly lead to the failure?

No.

You customer experienced a failure and since the purchase was from you, you are expected to make it right.

How deep is your supply chain?

You probably don’t know just how many suppliers are involved in converting raw material into your final product. Mining and processes, transportation, forming, assembling, Everything from the instruction manual copy (outsourced to professional writers?) to the packaging material use to ship the product to the customer (do you make your own cardboard from your own trees?), comes from one or more suppliers.

One way to visualize the complexity of your supply chain is to select one component and trace back to raw materials the location and distances involved. Something as common as a ceramic capacitor has maybe a 5 to 10 raw materials from metal layers to ceramic composition, to insulation, and marking. Maybe 50 different companies in an informal and changing chain create the capacitors you use on your circuit boards.

Cadmium Question

Years ago while working with HP I received a call from a customer. She asked if the HP desktop computers used any cadmium from specific mines in Africa. I had no idea, nor any good way to find out.

Sure cadmium is used in inks, electronic components. It was most likely in one or more locations within a desktop computer.

The exercise of just finding the source or likely sources for one element became educational at the complexity of modern supply chains.

Impact on Reliability

Unlike Henry Ford, we do not have iron ore mines, ships, smelting equipment, etc.

We don’t control our product from raw material to final product. We rely on each vendor the supply chain to optimize their product for their own good, which includes that their product works as expected for their customers.

Just like us looking back over the supply chain, vendor look forward wondering where and how their product is used. The miner’s of cadmium may have an idea of some of the uses of the material, yet are likely just as unable to answer the question about the cadmium content in a HP desktop as I was.

The result of this system is a breakdown in understanding concerning what is important concerning the quality and reliability along each step in the supply chain. Sure, we use specifications to communicate material purity or capacitance, for example, yet, that is what is supposed to happen.

It’s when a element in the process is not as it is expected that reliability problems occur.

Process Capability

No every vendor is able to consistently produce products within the specifications. We use process capability studies to measure the ability of a process to create product within specifications.

In some cases the impact is of little consequence. If the capacitance is 21% below the specification and we expected it to be within 20%, we most likely will not notice. If the capacitance is at 50% of the expected value, the circuit will likely not behave as expected, and most likely caught as when first assembled and tested.

It’s the changes that change the rate of change of the component, say capacitance drift or polymer creep, that go undetected until a short time in the customers hands. A small change in the material purity, or a change in process parameters, or an alteration of assembly steps, may initially seem fine.

It’s when the change causes a rapid deterioration of performance that we feel the impact of supply chain variation as a reliability problem.

We cannot control everything

So, what can we do? The supply chain is complex and includes many potential paths for reliability issues. Yet, there are a few things we can do, as reliability minded professionals to minimize the impact of supply chain generated failures.

First, establish clear reliability goals for each subsystem or major component. Know how long the parts of your product should survive and what is expected to fail. This increases your ability to communicate what is important to you supply chain, plus increase your ability to detect unwanted variation as it occurs.

Second, estimate or isolate the components from your supply chain the the highest risk. FMEA or other methods apply. So does engineering judgement. Consider the consequence of an individual component or a batch or all failing after 1 month, or after 6 months (exposure is important too.)

Third, determine the process capability for critical parts. While you should know Cp and Cpk for every part, we often have to prioritize. Use the results of the risk step (which is regularly updated as you learn more about the product design and the supply chain).

Forth, establish rigorous monitoring methods to insure the critical and high risk parts remain in control, stable, and as expected. Expand the monitoring to as many components as you can afford to manage.

Finally, for those process that are crucial to you products success, fully understand them. If this is your supplier’s supplier’ process – take the time to become an expert. Plus, for each failure encountered with prototypes and early production, again learn about the processes and materials variation that led to the failure. Root cause analysis should include understand the capability of the processes involved.

Your supply chain will significantly influence your field failure rate. You cannot inspect in reliability, so working to minimize variability and risks will support you goal to create a reliable product.