The communication between suppliers or vendors and their customers is often using a mix of specifications and requirements.
Customers set requirements and suppliers offer specifications. When they match, or when a supplier component specifications meet the customer’s requirements, we have the potential for a transaction.
Most products on the market include materials, components, or subassemblies, from other organizations.
The product development team conceives of a product concept then organizes the necessary elements to create a product.
Many of those elements are purchased.
Elements may be standard items, like bolts or capacitors, essentially bought off the shelf. Some elements are custom.
Custom elements may include drawings and extensively documented requirements.
Examples of custom elements of a product include the printed circuit boards and molded enclosure parts.
Reliability Requirements
The reliability requirements are the goal statement for the element.
If the cell phone has a system goal of 95% reliable over 5 years, then the main circuit board within the phone may have a reliability goal of 99% reliable over 5 years.
The development team may refine the environmental and use conditions specific for the element, in this case, a circuit board in order to fully describe the reliability requirements.
Just as when setting a reliability goal the apportioned goal for purchased elements require all four elements:
- Function – often detailed in a requirements document
- Environment – use conditions and profile details
- Duration – length of time or number of cycles
- Probability – likelihood of successfully functioning over the duration
Specific requirements for purchased elements of a product provide the supplier the necessary information to provide or craft an element of the product that enables the system to meet reliability goals.
If the supplier does not know the reliability requirements, they will attempt to provide a part that meets the stated requirements only.
The reliability performance will be uncertain.
Generally, suppliers desire to provide components that last longer than the products expected duration of use.
Suppliers do not want to field customer complaints that their element of a product is causing premature or early failures.
The more information the supplier has about the product and reliability goals, the more likely the supplier can provide a solution.
Reliability Specifications
Many components found in products have many applications.
Motors, power supplies, buttons, etc are examples of components found in cell phones, medical devices, industrial equipment, and vehicles. And in each application, the basic technology may be identical.
For example, a specific multilayer ceramic capacitor without modification may become part of your laptop computer or family vehicle.
The organization designing and producing the capacitors doesn’t know the final product application.
The supplier for non-custom parts crafts a data sheet which describes the functional, environmental, mechanical, electrical, and in many cases reliability elements of duration and probability.
The data sheet may provide a reliability statement under specific functional and environmental conditions.
The reliability statement may be as simple as a failure rate value, or a set of formulas describing the likely time to failure under specific stress.
This latter example is very rare, unfortunately.
Most reliability specifications are lacking one or more of the four elements of a fully stated reliability goal.
Ideally, the supplier can articulate the likely failure mechanism (how the component is most likely to fail) along with how the component responds to a range of stresses.
If a component would survive 20 years with a very small chance of failure if operated in a climate controlled environment maintaining a steady 30°C, or have a high chance of failure in 5 years if used in a 30°C swing in an hourly thermal cycling environment, that should be made clear.
Custom Parts
When a design calls for a custom part, the development team crafts the requirements and seeks one or more supplier to create an element that meets the requirements.
The supplier may add specifications, yet those are often just at or beyond the requirements.
The same is true for the reliability requirements discussion.
The supplier may attempt to exceed the requirements in order to have some margin over the requirements. Instead of creating a component that is exactly 99% reliable over 5 years, the supplied part may actually achieve 99.9% reliability over 5 years.
This is possible at times, and sometimes not so due to technology or economic constraints.
Ideally, the requirements include the necessary reliability elements that are consistent with the overall system requirements.
Plus, the supplier provides elements the meet or exceed the expected reliability performance.
This really only can occur if the two parties communication the expectations and capabilities clearly.
We already use requirements and specifications to start these conversations.
Now look closely at those documents and make sure they include the reliability elements that make the reliability performance clear for both parties.