Feature
r When Franchisemanager at Solid State
Supplies, Alan Hebdon, answers the top five purchasing questions regarding high reliability components
1. What is the difference is between a COts part and a mil COts part?
There are two types of commercial off the shelf (COTS) parts: MIL COTS and normal COTS. The normal COTS component is usually a plastic commercial device, probably RoHS compliant and in need ofmoisture sensitivity level (MSL) controlled storage conditions. In the case of both hermetically sealedMIL COTS devices and any through-hole components, this requirement does not apply, which can reduce the necessity to rebake components if anymoisture ingress takes place.
AMIL COTS part will be the same as themilitary specification
(mil spec) device but without any screening, so if themil spec part is hermetically sealed, so is theMIL COTS part. There is a tendency to purchase COTS parts for potential cost savings, but we always advise customers to check what they are being offered and to ensure its suitability for the application.
As a word of caution, there can be more than one part
number, or a different part number for aMIL COTS device, compared with the military equivalent. If in doubt, seek expert advice.
2. What opportunities exist for product substitution when specifying screened parts?
WithMIL COTS, JAN screened parts or JANTX screened discrete components, it is normally OK to accept a higher level of screening. For example, a JAN screened part can be substituted with a JANTX or a JANTXV part, or a JANTX part replaced by a JANTXV part. The components are electrically andmechanically the same butmoving to the next level of testingmeans that you are buying a potentiallymore rugged and reliable device.
Bear inmind, however, that end usersmay specify the
screening level required very precisely, so caution should be exercised before substitute parts are purchased. As a rule, the higher the level of screening, the higher the price you would expect to pay, but the differences are not always large and
eliability is amust
Franchisemanager at Solid State Supplies, Alan Hebdon, helps purchasers understand military and aerospace jargon
April 2011 | 19 p20
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