General Information

Drum Side Treated Foil (DSTFoilÒ), Polyclad's patented copper foil technology, is designed for the most demanding fine-line, tight-spacing innerlayer technologies. DSTFoilÒ and traditional copper foils used in multilayer Printed Wiring Boards (PWBs) are manufactured using the same basic process. Both types of foils are made by electroplating copper onto a highly polished drum. The resulting raw copper foil has a very smooth, shiny surface on the drum side and an inherently rough, matte surface on the other side. Traditional copper foils are treated with a secondary copper plating step on the rough, matte side to further increase surface area followed by a non-reactive barrier layer also on the rough, matte side and an anti-corrosion passivation coating, typically applied to both sides. DSTFoilÒ differs in that the secondary copper plating step and non-reactive barrier layer are applied to the smooth drum side. With both types of copper foil, the treated barrier layer side of the foil is laminated to the inside of the multilayer core laminate. Figures 1 and 2 show the differences between laminates produced with traditional copper foil and DSTFoilÒ.

Figure 1 -Laminate clad with traditional copper foil

Figure 2 - Laminate clad with DSTFoil

Laminates produced with traditional copper foil have very smooth outer copper foil surfaces with the rough treated copper foil side against the core. Laminates produced with DSTFoilÒ have a naturally rough, matte outer surface with a lower topography surface against the core. These differences with DSTFoilÒ clad laminates have important advantages. The naturally rough, matte outer surface provides a superior surface for resist adhesion without the need for subtractive chemical cleaning or mechanical roughening of the surface, although chemical cleaning of the DSTFoilÒ surface is still recommended. This improved resist adhesion reduces the chance of opens, mouse bites and etchouts. The naturally rough surface also requires no subtractive cleaning during the oxide or oxide replacement process and results in higher prepreg-to-copper bond strengths. The low profile topography against the core makes small spacing resolution easier and more predictable without the need to over etch, which improves line side wall geometry and reduces the chances of unetched copper and shorts. Taken together these differences result in improved inner layer yields, process cost reduction opportunities, potential copper waste stream reductions, better product consistency and measurable, better overall PWB performance.

AVAILABLITY
All Polyclad laminate grades are available with DSTFoilÒ cladding. Standard DSTFoilÒ copper cladding is available from 3/8 ounce (12 micron) to 3 ounce (103 micron). Other DSTFoilÒ copper cladding weights and thicknesses are available by special request.

PROCESSING AND STORAGE
Processing of laminates clad with DSTFoilÒ is identical to that of laminates clad with traditional copper foil. To take full advantage of all the opportunities provided by DSTFoilÒ, some process adjustments might be required to achieve optimal performance. For specific processing guidelines and recommendations, please contact Polyclad Technical Services.

Storage of laminate clad with DSTFoilÒ is the same as for all FR-4 copper clad laminate materials. More detailed storage recommendation technical bulletins are available from Polyclad.

APPLICABLE SPECIFICATIONS AND RECOGNITIONS
Polyclad's UL file number is E45456. All Polyclad laminate grades clad with DSTFoilÒ are certifiable to the appropriate designations and listings. Certain other more specific parts of Polyclad's UL listing may be applicable in some cases. Laminates clad with DSTFoilÒ meet all the requirements of and can be certified to the applicable Specification Sheet of IPC-4101, Specification for Base Materials for Rigid and Multilayer Printed Boards. DSTFoilÒ meets all the applicable type and grade requirements of IPC-MF-150, Metal Foil for Printed Wiring Applications. Other industry or customer specific specifications, recognitions or designations may be applicable or certifiable to in certain cases. If you need additional information or have questions, please contact Polyclad Technical Services.