Takahiro Tanabe

Profile-Free Copper Foil for High-Density Packaging Substrates and High-Frequency Applications

A new profile-free copper foil has been developed whose surface roughness is Rz <1.5 mum with satisfactory adhesion strength. An original surface treatment provided affords good peel strength (0.7 kN/m or more) equivalent to that for the conventional roughened foil with sufficient reliability. With the new profile-free copper foil, the conventional subtractive method is applicable to the wiring of 60 mum pitch or less, and the short-circuit fault of electroless Ni/Pd/Au plating that is prone to occur in fine wiring could be restrained since the wiring is formed on a smooth surface. Moreover, the transmission loss at 5 GHz band is decreased by 8 dB/m since the surface roughness of the conductor line is suppressed

The new primer with copper foil corresponding to semi-additive process for package substrates

The demand for downsized and light-weighted electronic parts has become stronger to realize the higher electrical performance and smaller size of electronic equipment. Thus, the package substrate used in electronics is demanded to be thinner and higher in wiring density. Generally, semi-additive process using insulating film is used to form lines finer than line/space: L/S=20/20 μm in the package. The problem is that the thinner insulating film is likely to cause the higher warpage due to the higher coefficient of thermal expansion (CTE) and lower modulus. The applying glass-fabric prepreg to outer-layer of the package may result in the lower warpage, but it is difficult to make finer lines less than L/S=20/20 μm [1]. We started to develop the new primer with a copper foil (PF-EL) having high adhesion property with electrolessly plated copper and glass-fabric prepreg. After laminating the PF-EL with glass-fabric prepreg, the copper foil is etched out. Then, the surface of appropriate roughness made by replica of the copper foil profile is remained on the primer. The primer with appropriate roughness is applicable to semi-additive process, resulting in the higher wiring density and lower warpage for package substrate. In addition, PF-EL can be also applicable to the conventional press process without the laminator process. The peel strength of PF-EL for electrolessly plated copper is equivalent to that of the chemically roughened insulating film (0.7 kN/m or more), the sufficiently enough value for the excellent reliability. This higher peel strength is achieved by chemical functional groups and the optimization of curing degree of primer resin. The line/space of the fine line obtained with the primer is L/S=10/10 μm.

Epoxy adhesive sheet with copper foil for multiple IVH build-up technology

The interstitial via hole (IVH) structure, in which the interconnections of signal layers are designed with nonthrough holes, is strongly focused to meet the need for small and high-performance electronic equipment with thinner and high wiring density multilayer boards (MLBs). A new epoxy adhesive sheet with copper foil was developed for multiple IVH build-up technology. Since no glass cloth is used for reinforcement, the adhesive sheet allows IVH structure fabrication by CO/sub 2/ laser ablation. It has superior resin flow properties for filling both inner-pattern and inner-layer IVH structures. The surface flatness of the build-up layer with this new sheet allows very fine wiring patterns on to be fabricated. This sheet, which does not concave during the wire-bonding process since its surface is hard at high temperature, is suitable for MLBs with semiconductor chips. This material is effective for manufacture of thin MLBs with IVH structure and high wiring densities.

New halogen-free laminate for advanced package substrate

Nowadays, the demand for the printed wiring board (PWB) of the environment harmony type is rising rapidly. We have developed a new halogen-free material with low coefficients of thermal expansion (CTE), which will be applied to the plastic packages such as FC-BGA and CSP. The original resin system and filler treatment technique named FICS (filler interphase control system) were applied to the material. The newly developed halogen-free material named MCL-E-679FG(S) has a higher glass transition temperature (Tg), peel strength, and heat resistance than the conventional halogen-free materials. Their properties are advantageous to the melting temperature rise of the lead-free solder. Another newly developed halogen-free material named MCL-E-679GT has the lower CTE combined with standard glass fabric (E-glass). It has been developed by new resin system. Its advantage is to reduce of PKG warpage, such as package on package (PoP), during the heat process for the chip mounting. In order to meet fine-line formation, we developed profile-free copper foil. With the copper foil of 18 mum thickness, we have formed the fine line of 60 mum or less pitch by the conventional subtractive method. It will be effective for advanced package substrate such as high density CSP.

New halogen-free high elastic modulus build-up material

The authors have developed a new build-up material MCF-6000G, which has high elastic modulus and has the incombustibility of UL94 level V-0 without halogenated flame retardant. Applying high Tg epoxy resin and a special fibrous filler gave high elastic modulus. The halogen free incombustible system was achieved by combining the following techniques: adoption of aromatic-ring rich resin and carbonizing catalyst; addition of suitable metal hydroxides and fibrous filler; high density filling and filler/resin interface control. MCF-6000G contains no halogen and has a high elastic modulus, high Tg, low coefficient of thermal expansion (CTE), and sufficient processability. It will be a promising environmentally-friendly material for PWBs.