Reverse treated copper foil is manufactured by applying copper nodularization, brass thermal barrier and passivation to the shiny smooth side of the foil rather than to the roughened matte side of the foil as is done when manufacturing conventional copper foil. A thin layer containing only passivation or anti-oxidants, which is the same to the shiny smooth side of all GOULD copper foils, is applied to the roughened matte side of reverse treated foil. The fully treated drum side can be laminated to prepregs of a broad range of resin systems. Reverse treated foil is the best choice for fine-line inner layer processing.
Reverse treated copper eliminates the need for aggressive precleaning of laminates by mechanical or chemical means. A simple wash with 10% sulphuric acid removes the passivation leaving the roughened matte surface available for photoresist processing.
The VLP treatment of RTCHTE foils compared to standard Grade 3 provides faster, cleaner etching with more vertical sidewalls. Inner layer yields can be higher due to the cleaner etching and less undercutting of photo-resist.
The already roughened matte surface of reverse treated foils eliminates the need for microetching or roughening during oxide processing. The costly waste disposal associated with microetching is, of course, eliminated with RTCHTE.
The foils exhibit excellent ductility at elevated temperatures,and eliminate foil cracks near the plated through holes for dense MLBs with very high layer count.
Foils are formulated to resist recrystallization or grain growth after thermal processing which could degrade laminate dimensional stability, warp & twist and drilling characteristics (nail heading).
Foils are formulated with a balance of tensile strength for good handleability and ductility for high resistance to inner layer foil cracks.
GOULD's thermal brass barrier layer on treated drum side acts as a physical diffusion barrier preventing any adverse chemical reactions with the resin system and stabilizes bond during thermal aging.
Generally, the bond strength of reverse treated foils is lower because of its very low profile treatment when compared with standard treated foils. But, the fine nodular TC treatment guarantees sufficient mechanical adhesion to a broad range of laminating resins and is supported by a tailored silane treatment.
All properties meet and exceed the requirements of IPC 4562, Grade 3.
|1) Without plating up|
|Property||Unit||RTCHTE (RTCS) - Grade 3|
|Peel strength FR4-TG 140||N/mm||>1.051)||>1.101)||>1.42||>1.88||>2.20|
|Treated shiny side, Rz||μm||<5.1||<5.1||<5.1||<5.1||<5.1|
|Untreated matte side, Rz||μm||2...4||3...5.5||4...6.5||7...12||9...15|
Reverse treated foils are routinely available in continuous rolls and sheeted formats. Roll products can be supplied in a variety of widths and thicknesses from 12 μm (0.375 oz/ft2) to 105 μm (3 oz/ft2) on cardboard cores with an ID of ~ 79 mm (3 1/8”) or 152 (6”).