A novel FR-4 material for embedded substrate

Abstract

Two processes of components embedding, both active dies and passive components, have been demonstrated so far — one is the embedding of chip by ABF/RCC material, and the other is the embedding by multiple plies of prepreg with machined cavity of placing component. ABF/RCC materials appear to the most straight forward way to embed components into PCB. The drawback is that the components to be embedded have to be thinned to 50μm but this is not practical for all types of components, and also the cost is very high. Multiple-ply prepreg with machined cavity can accommodate die of various thickness and thus offer more choice of different component thickness. However they do not get wide acceptance because of the low throughput and the concerns over the yield. To address the problem component embedding and offer the solution, Atotech has developed a novel process of manufacturing FR-4 material. This novel process, named “Advanced Dielectric Epoxy Powder Technology (ADEPT)”, is a solvent-free production technology. The dielectric is made of powder and is later coated on the copper foil. The final form is a resin-coated copper foil (RCC.) Moreover, the glass fabric can be laminated into the RCC, making it a Reinforced Resin-Coated Copper foil (RRCC.) The materials have passed reliability tests required in PCB and assembly industry, which include lead-free assembly, MSL, HAST, CAF, and TCT. By ADEPT, a multi-layer material, in sheet form, can be produced for the embedded substrate. First, a reinforced dielectric layer with glass fabric will offer good dimension control. Second, an additional resin layer, with high filler content to reduce CTE, will be used for component embedding. With the multi-layer material, the process of component embedding can be done in one go, without having the drawbacks of the large warpage by ABF, or the step of the cavity formation required by multiple-ply prepreg. After component embedding, the reinforced layer effectively minimizes the warpage so the panel can be laser drilled and processed. Finally an ultra thin, low profile copper foil will be ideal for modified Semi-Additive Process (mSAP), a way of fine line structuring at relatively low cost. Since by ADEPT the dielectric is made of powder, it soon lends itself easily to the molding process in assembly. Its advantages over molding compounds are the capabilities of form small (50μm) laser vias due to the selection of sub-micron filler (Max./Mean filler size=1.0/0.3μm) and it is compatible with e'less copper deposition. As close partners, Atotech and ASE Global are exploring the applications of this dielectric powder as a molding compound for component embedding process.