It is generally accepted
that over 97 percent of all product failures will occur in the first
24-hours of operation. Product burn-in “infant mortality” in finished
goods is one of the biggest problems facing electronic product
manufacturers. Burn-in plays a critical part in ensuring products
delivered to the market are reliable and will not fail.
200,000 of a given product manufactured with an infant mortality rate of
0,5 percent means that 1,000 units could be expected to fail in the field.
Burning in for 24 hours reduces this figure by 97 percent or more giving
an expected field failure of only 30. “This is a vast improvement
from 1,000 failed units,” explains Murton System Technologies MD Brent
Maurer, Turnkey Manufacturers of electronic products, sub-assemblies and customized
development projects. After this, manufacturers experience diminishing
returns for the length of burn in time.
manufacturers, independent test labs, end-users and Turnkey Manufacturers
normally perform burn-in. Sample units of new devices or new lots
are burned in to provide reliable data for the remaining devices.
At the component level, burn-in
is done by loading devices into high temperature sockets, which make
temporary electrical contact with the device leads, and are mounted on
high temperature circuit boards with circuitry to provide the proper
voltages and stimuli to the device. The devices are isolated from
one another with passive components, which limit the current each device
The boards containing the
devices are then loaded into a convection oven which elevates the
temperature of the device and provides an electrical interconnect to the
power supplies and signal generators. The devices remain in the oven
for an amount of time determined to induce failure. The rate that
these devices fail is called the infant mortality rate.
Most ICs consist of ion
junctions implanted on silicon substrate. The junctions are
connected with small traces of conductive oxides. The ambient heat
and the heat caused by current flow causes the junction temperature to
rise. This causes ion 'clouds' which surround the junctions which
dissipate from their original locations.
These stresses can lead
to premature failure of weaker devices. They can also lead to the
failure of non-marginal devices, if the junction temperature exceeds the
manufacturers’ maximum rating. At the "end of operational
life", the heat of burn-in has caused the ions to dissipate to the
point where the devices no longer functions.
There are two types of
burn-in, lot sampling and operational life testing. In burn-in, all
of the devices of a particular type are burned in to 'weed out' the weak
devices. Lot sampling is a technique where a small control sample is
burned in and the statistical data derived from testing those devices is
used for the remaining devices of the lot.
“Different types of
burn-in are designed for different types of devices. We use
static-burn-in as well as dynamic burn-in, both during the design phase
and production phases, and test during as well as after burn-in for device
system deviation tolerance and failure. This enables us to ensure
that we are able to ship goods of consistently high export quality and
that potential design flaws are detected during burn-in and rectified,”