Obsolete passives: no bid or no problem?

Roger Tall, director and product specialist

To find alternatives to obsolete or allocated capacitors or resistors, a distributor must commit knowledge, resource and time says Charcroft’s Roger Tall

When a distributor receives an enquiry for an obsolete capacitor or resistor, the fastest and easiest response is a no-bid. For the distributor, this is a simple way of avoiding the work of finding an alternative. For the customer, it represents a dead-end and means extra work to find the part from another supplier or try to find a viable alternative.

The customer may be able to source the obsolete passive from an unfranchised source or the grey market. The customer then faces the added risk of losing full component traceability. The part could have been compromised by unsuitable storage or recovery from existing hardware nearing its end-of-life.

Instead of no-bidding, the distributor should accept responsibility for identifying an alternative. Providing this service is an essential part of developing and maintaining a long-term customer partnership.

Obsolescence is not the only reason buyers may find passives hard to source. As lead-times have extended, some passives are on long lead-times or allocation. Sourcing these passives is similar to sourcing an obsolete part. So, the distributor should automatically deliver the same level of skill and commitment to identify an alternative solution.

The process of identifying an alternative begins with knowing the part’s full specification. Some bills-of-materials will only show a part number or even the internal part number used by some defence OEMs. The first step is finding the datasheet and checking the detailed parameters.

The challenge is that most distributors focus on fast-moving, high-volume markets. How many have kept copies of original datasheets for parts specified years or decades ago? Unlike non-specialist distributors, Charcroft has always focused on supporting customers in the military, aerospace and other demanding markets, where the end products have exceptionally long lifetimes.

This is why Charcroft has a digitised archive of every datasheet it has received over the past 50-years. Finding a full specification is just a matter of checking a datasheet possibly printed in the 1970s.

Defence OEMs’ internal part numbers are also archived, so when a legacy internal part number appears on an enquiry, it can be cross-referenced to the component manufacturer’s original part number.

This archive is a vital resource for finding replacement passives. Once the product description is known, it can be matched to an available part number from a different manufacturer or to its mil-spec part number.

An alternative can often be found by checking each parameter of the original against the required performance. Critical systems in defence, military, space or high-end industry need to be failure-free but that does not mean every component, in every system, needs the maximum possible screening offered by the mil-spec.

Every aspect of the passive component must be examined, from capacitance or resistance, to temperature, voltage, stability and packaging.

Must the replacement match the one per cent tolerance specified or was this a standard practice to specify passives to a tight tolerance? If the tolerance can be relaxed to five per cent, without compromising performance or reliability, the number of possible alternatives becomes larger.

If the obsolete passive was specified in a metal case, the replacement could be in a plastic case with an epoxy end-fill to maintain reliability.

Where no available alternative can be identified, another solution may be to manufacture a custom passive assembly. One custom assembly, manufactured by Charcroft in the UK, combines one capacitor and two resistors from different manufacturers to provide a solution. These components were assembled in a series/parallel combination and encapsulated in a plastic case.

Custom assemblies can replace an obsolete passive by combining a deep knowledge of the demands of harsh applications, with an understanding of legacy and modern passive component technologies. Lateral thinking is often needed.

No-bidding on obsolete passives can be overcome if the distributor is prepared to dedicate the required time, skill and resources. It is not easy but is essential for a strong customer/distributor relationship. This is particularly important for customers buying passives for critical systems expected to perform reliably over many years.

The distributor must be prepared to dedicate specialist knowledge and resource, and work in partnership with customers and component manufacturers, to source alternative solutions. No bid should be replaced with no problem.