Hi TechNetters,
We just finished discussing copper foils and the shortcomings observed in
product.
Currently, a new IPC document, IPC-6013, Qualification and Performance
Specification for Flexible Printed Wiring, is being circulated for comments.
In it, under 3.2.5 Metal Foils, "copper foil should be in accordance with IPC-
MF-150, which is modified in 3.2.6.2 Copper with "the tensile strength shall
be no less than 245 MPa and the elongation shall be no less than 12%."
While the modification is a step in the right direction, it should be part of
section 3.2.5, not detached from it. Technically, requiring an elongation of
12%, rather than the 2 or 3% minimums in MF-150, is also appropriate. However,
why specify elongation. For comparative and process control purposes,
elongation is fine, however, it has long been recognized as an inadequate way
of determining the actual ductility of foils. From a sample geometry of foil
tensile test samples makes the measurement of ductility by this method
impossible. Further, the results are highly dependent on testing technique.
That is why ASTM E 796, "Standard Test Method for Ductility Testing of
Metallic Foil" and IPC-TM-650, Test Method 2.4.2.1,“Flexural Fatigue and
Ductility, Foil,” were developed.
I urge interested TechNetters to ask for the following TECHNICAL CHANGES:
(1) Ductility as per TM 2.4.2.1 should be specified;
(2) Combine Sections 3.2.5 and 3.2.6.2;
(3) Include Table A1 'Applications Guide for Copper Foil' which distinguishes
between the difference needs for 'Flex-to-Install' and 'Continuous Flexing',
or something like it.
Werner Engelmaier
Chairman, IPC Product Reliability Committee
Past Chairman, IPC-MF-150 Task Group
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