Arlon identify one of the most common failures in these boards as delamination at the foil surface due to adhesion failure. This occurs because the rolled CIC foil is smooth, with little surface area available for bonding. Even building an oxide film on it does little good. The only satisfactory way to achieve adhesion is to use a treatment that creates a very uneven surface structure. Arlon’s proprietary process gives a key to the prepreg that is sufficiently strong for the weakest link then to become the bond between surface treatment and foil, and this is adequately strong to withstand the stresses of thermal cycling.
A second problem comes from clearance holes in thick (150 µm) foil. Filled with resin from prepreg, this can result in cracking and give problems with plating and Z-axis expansion. Arlon suggest filling such holes with a more compatible resin system.
Arlon also reinforce the need for balance in the lay-up in order to avoid severe warping problems during processing. CIC foils must be used on both sides of the board, and never used either for single-sided boards or in combination with a copper foil on the reverse of a double-sided board.
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