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.
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 treatment of RTC foils compared to standard foils 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 RTC.
Foils are formulated with a balance of tensile strength for good handleability and ductility for high resistance to inner layer foil cracks.
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 1.
|1) Without plating up|
|9 μm||12 μm||18 μm||35 μm||70 μm||105 μm||140µm||175µm||210µm|
|Peel strength FR4-TG 140||N/mm||>1.001)||>1.051)||>1.181)||>1.69||>2.28||>2.75||-/-||-/-||-/-|
|Treated shiny side, Ra||μm||<5.1||<5.1||<5.1||<5.1||<5.1||<5.1||<5.1||<5.1||<5.1|
|(untreated) matte side, Rz||μm||2...4||2...4||3...5||4...6.5||7...10||8...12||<14||<16||<18|
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 9 μm (0.25 oz/ft2) to 210 μm (6 oz/ft2) on cardboard cores with an ID of ~ 79 mm (3 1/8”) or 152 (6”).