Excerpt from IEEE paper "SHELF LIFE OF ELECTRONIClELECTRICAL DEVICES" by Salvador Polanco and Anup K. Behera
A. Transistors - The samples were tested according to their
date, the initial measured Beta Value for the as-found condition and the final measured Beta value were subjected to 150 continuous hours at 212'F .
The transistors under test had date codes ranging from
1966 to 1969. Therefore considering the accelerated aging
test, the equivalent storage time is 66 to 63 years. Based on obtained, and taking into account the information available from industry testing with the items energized, transistors can effectively be consideredl to have an indefinite shelf life by implementing a 40-plus year storage capability.
B. Electrolytic capacitors were measured after
reforming. Samples were subjected to two accelerated aging
cycles, others for three aging cycles depending on the
manufactuliag date codes. Based on the test data, the capacitors were artificially aged to simulate the equivalent storage time of 24 (two aging cycles) and 36 years (three aging cycles) by being subjected to 185'F in a laboratory oven as described in Section 111. This supplemented their natural aging time which results in an
equivalent life of 49 to 54 years. The testing will continue
until the capacitors fail to reform. However, for pupom of
this evaluation, the shelf life of the electrolytic dielectric capacitors is considered to be indefinite.
C. Silicon Controlled Rectifiers. Varistors and Resistors -
The material of construction of SCRs is similar to the rest of the silicon semiconductors family which has been proven to be indefinite. The material of construction of varistors is a metal oxide base which is known to be age insensitive. Carbon and film resistors have been proven by industry tests ta last for 70 and 230 years, fully energized at an equivalent temperature of 80'F. For the above mentioned reasons and based on engineering judgement the SCRs, varistors and resistors can be considered to have an indefinite shelf life.
END OF EXCERPT
To this, one could add that electrolytic capacitors usually need to be "reformed" after prolonged storage and that some early CMOS processes had problems with "purple plague".
Moisture is an enemy to most components and diffusion as well as capillary seepage can be a problem. But, if stored in a dry environment, the shelf life should be as said above.
One special aspect of shelf life is solderability. That is definitely something that degrades very quickly when components are stored. Hermetically closed containers are known to delay the process.
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