Message
how many thermal cycle in total over the
duration of 3500 hr? if it is less than 2,000, it is not stringe at all
for end of life test.. (hi-rel product), consider the temp range is not that
high (-30 to +80 = 120 C overall... Assuming non
condensing...).
jk
A
customer of Metallic Resources (manufacturers of bar solder) assembles circuit
boards. One of the many tests the boards go through is a thermal cycling
test to see if thermal shock can cause failure in the circuit
board.
The customer's test specification is Spec Number TSC7514g,
section 5.4, reference specification TSC 7010g. (We do not know what
this means.) The customer cycles the circuit board from -30 degrees
celcius to +80 degrees celcius. The board temperature is dropped to -30
and held for thirty minutes. The board temperature is then raised to +80
and held for thirty minutes, until the temperature is lowered again and so
forth for a total of 3,500 hours. The customer is now noticing solder
joint failures on this double sided board on the top, which is both
through-hole and SMT (failures of solder paste joints on the top), and on the
bottom, which is just through-hole (failures of bar solder joints).
Solder joints, both top and bottom, show much cracking and some flux
residue.
The first question is: is this customer using their own test
or is there an IPC test for thermal cycling of a completely assembled circuit
board?
The second question is: is the customer's temperature range too
extreme, which is causing severe thermal shock, which is then causing joint
failures due to different co-efficients of expansion and contraction
(board, solder, lead)?
The third question is: is the use of 3,500 hours
of thermal cycling realistic and/or too long?
Any comments would be
appreciated.
Sincerely,
METALLIC RESOURCES
Howard P.
Stevens
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