IPC-2223-Design-Standard-for-Flex-and-Rigid-Flex-Circuits.pdf - 第7页
Important Element #3 Adhesiveless Flex Cores The ex core materials used play an important part in meet IPC 2223 requirements. Flex cores are available in two congurations that dier in how the copper is attached to th…
Correct selective coverlay (left). Coverlays engage rigid areas by approximately 0.025”.
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A SELECTIVE COVERLAY CONSTRUCTION IS
ALSO KNOWN AS A “BIKINI BUILD” SINCE THE
COVERLAYS COVER ONLY WHAT NEEDS TO BE
COVERED, THE FLEX SECTIONS.
Important Element
#3
Adhesiveless Flex Cores
The ex core materials used play an important part in meet IPC 2223
requirements. Flex cores are available in two congurations that dier in
how the copper is attached to the polyimide core. The original generation
ex cores utilize a exible adhesive to bond the copper layer to the
polyimide. The latest generation has the copper directly attached to the
polyimide without the use of an adhesive. This material is referred to as
“adhesiveless” throughout the industry.
IPC 2223 specically calls out the use of adhesiveless ex cores only.
As the ex cores exist throughout the entire part using adhesiveless ex
cores eliminates a source of adhesive from within the rigid areas and the
associated via hole reliability concerns dened earlier in this Ebook. An
added benet is the reduced thickness, improved exibility and improved
bend reliability of thinner adhesiveless ex cores.
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SPECIFY ADHESIVELESS FLEX CORE BY THE
IPC SPECIFICATION IN THE DRAWING NOTES
AND GRAPHICALLY IN THE MATERIAL STACKUP
IN THE FABRICATION DRAWING
Adhesive flex core (top), adhesiveless flex core (bottom).