Copper Foil mechanical fatigue in flexible printed
circuitssubject to high cycle vibration
04/22/2009Don Blanchet3B Associates339-234-3544
Scope Present information on the
metallurgical structure of 2 copper foil structures used in flex circuit design for a vibration environment– RA, rolled annealed– ED, electrodeposited
“Superflex” from OAK-Mitsu
Metallurgical Factors Copper foils have grain structures that vary widely
depending on the manufacturing process
My research has found that they do not behave as does bulk copper both in the annealed and cold worked states
Foils developed for flex circuit applications are sometimes tailored for the type of flex and expected number of cycles
Specific Cycling Tests have been developed to determine fatigue properties for various common applications such as:
– Disk drives– Cellular telephones– Printers
Reference copper foil fatigue characteristics (1/2 oz)
LongCrack propagation
length
shortCrack propagation
length
Superflex copper
Is “SuperFlex” right for a vibration application?
Interviews with OAK-MITSUI tech support:
this material was developed for primary use in cellular telephone applications – large bend-to install and moderate flexure cycles.The last fatigue test was performed over 10 years ago to certify to IPC 4562 grade 11Our application sounds like a misapplication due to the number of cycles accumulated during our vibration testing They have never encountered a similar application
Hitachi copper foil research
Crack microstructure
“RA”
“ED”
Fatigue Life - vibration
~12 Hr qualification test
Conclusion Rolled and Annealed copper foil is
the clear choice over electrodeposited metallurgy for a high cycle flex application.
Goals Characterize the modal
frequencies.
Examine the response to Qualification level sine vibration 10G over 20-2000hz.
Look at 3 mutually perpendicular input axes.