Photopatternable Laminate BCB Dielectric

Abstract

Divinylsiloxane-bis-benzocyclobutene (DVS-bis-BCB, or BCB) is a well-known dielectric material that has been used in high volume manufacturing for many years (Dow's CYCLOTENE™ 3000/4000-series Advanced Electronic Resins). Typically, the application of these products has been by spincoating or spray coating of the dielectric material from a solvent-based formulation. However, for certain applications - for example, those involving large area, square substrates such as glass panels - it is desirable to be able to apply the BCB-based dielectric material using a dry film coating process, such as vacuum or hot roll lamination. In this paper, we describe the concept of creating a laminate film utilizing DVS-bis-BCB as the primary dielectric material component. In creating the laminate dielectric material, it is important to maintain the unique combination of thermal and electrical properties of DVS-bis-BCB, including high thermal stability, excellent copper barrier properties, low moisture uptake, low dielectric constant, and low dielectric loss. However, DVS-bis-BCB alone is too rigid to produce a high quality laminate film, therefore, it is necessary to modify the formulation to improve flexibility and lamination quality. As the flexibility of the film is increased, higher fracture toughness (K1C) and higher elongation values should result. Novel formulation adjustments to the base DVS-bis-BCB polymer system have resulted in an experimental laminate dielectric product that will be the focus of this discussion. Depending on the application, laminate films can vary in thickness from 2μm to 50μm or even thicker. A typical laminate film construct includes the BCB-based dielectric film with a base sheet of an optically-clear polyester (PET) film and a polyethylene (PE) cover sheet. The DVS-bis-BCB-based laminate can be tuned with appropriate additives to either pattern with UV exposure from a tool such as a Süss MicroTec Mask Aligner (50mJ/cm2 – 100mJ/cm2 exposure energy) or laser pattern with a tool such as a Süss MicroTec 248nm Excimer Laser. Aspect ratios of 1:1.5 have been achieved with a photopatternable DVS-bis-BCB film and aspect ratios of >1:1 are possible with a laser-patterned film. Beside the photopackage added to the film to enable UV patterning, toughening additives have also been incorporated to enhance the fracture toughness (K1C) and elongation properties. K1C for the laminate has been improved to 0.55Mpa·m1/2 vs. 0.35Mpa·m1/2 for DVS-bis-BCB. Elongation has been improved to 13% for the laminate vs. 8% for DVS-bis-BCB. Electrical properties are similar to DVS-bis-BCB. An additional attribute of the laminate dielectric is the ability to tent over and protect vias. Vias >100μm diameter have successfully been tented with a 10μm thick film. A DVS-bis-BCB-based laminate has been demonstrated with continued optimization and evaluation to follow.