The criteria currently used by industry to cover the screening of components
are based on the reliability requirements defined in paragraph 4.2. However,
there are many variations to the actual levels and degrees of control imposed on
the component manufacturers by the power supply manufacturers. Nonstandard
components are addressed by the controls placed by the power supply
manufacturers in their procurement specifications. Modified standard components
are likewise controlled but only for selected items and/or parameters.
Generally, there is substantial commonality among most companies that design and
manufacture power supplies such as:
(1) Controls to evaluate vendors based on performance and history
(2) 100% or sample testing done at the power supply manufacturer's receiving
(3) Sample Destructive Physical Analysis (DPA) and/or periodic inspection.
This is usually done under contract direction from the power supply
(4) Emphasis on solderability
(5) Certain components that have historically been a problem are either
avoided or limited
(6) Components are characterized by the power supply manufacturer for
construction as well as electrical performance in order to determine their
strengths and weaknesses. This is typically done before a component is committed
for use in a product.