Adhesion Study between Electroless Seed Layers and Build-up Dielectric Film Substrates

Abstract

The adhesion between the electroless seed layer and the buildup film substrates was studied. After the buildup film was laminated, the buildup film surface was modified by a desmear treatment from 0 to 30 min, and electroless Cu or electroless Ni-P was plated as the seed layer on the buildup film. The Cu was then electroplated, and the post curing was carried out at 180 • C for 2 h before or after Cu electroplating. The adhesion strength between the electroless seed layers and the buildup film substrates was measured by the 90 • peel test. Increasing the desmear treatment time made the buildup film surface rougher, and consequently enhanced the adhesion strength of the electroless Cu and electroless Ni-P to the film. Under the same conditions, the electroless Ni-P specimen showed a higher peel strength than the electroless Cu specimens. Post curing significantly increased the adhesion strength due to the increased ductility of the metal layer after heat-treatment. In addition, the peel strength decreased as the thickness of the seed layer increased, which was also related to the mechanical properties of each metal layer.Electroless metallization is widely used for the fabrication of circuit patterns in microelectronics because electroless plating can deposit on wide variety of materials including insulating surfaces such as glass, oxides, and polymers, without the need for any electrical equipment. 1,2 However, the electroless plating of metal on polymer substrates is often limited by weak adhesion strength caused by structural incompatibility between the substrate and the metal layer. The finer dimensions of the typical interconnection pattern obtained from the buildup film has made even the reliability of packages critical; therefore, good adhesion of the metal on the buildup insulating films is essential. 3,4 Cu metal has been widely used in semiconductor manufacturing due to its high conductivity and low cost, 5,6 and electroless copper is usually deposited on the buildup insulating film as a conducted seed layer for subsequent Cu electroplating. In order to improve the adhesion of plated copper on the polymer film, many processes involving plasma activation followed by surface graft polymerization have been carried out. 7,8 However, compared to plasma processes wet chemical treatments are preferred industrially due to the much lower cost. 3,9 A typical wet chemical processes for the pretreatment of buildup film consist of three steps: swelling, desmear and neutralization. 10 After pretreatment, mechanical interlocks that utilize anchoring sites on the roughened surface of the buildup insulating film enhance adhesion. 3,9,10 Electroless nickel has also been studied as a potential conducted seed layer deposited on buildup film for Cu electroplating. 8,11 However, even though many techniques has been developed to enhance the adhesion of the metal layer to the insulating substrate, previous research has mainly focused on the interfacial energy effect such as chemical bonding. However, the mechanical effect of th...

Improvements of the Epoxy–Copper Adhesion for Microelectronic Applications

“…Figure depicts the peel strengths and the corresponding R MS values (prior to electroless copper plating) against the degree of precuring (only for α > α gel since the whole ABF were dissolved for lower α). At low degrees of precuring, the peel strength values are comparable to the literature. ,,− The peel strength gradually decreases with increasing degree of precuring to reach a value smaller than 1 N/cm for α > 0.8. At higher degree of curing (α > 0.85), several spontaneous delaminations were observed for about 80% of the samples area (in these cases the peel strength values were considered null), leading to low peel strength averages with large error bars.…”

“…The buildup layer studied was an Ajinomoto buildup film (ABF) by Ajinomoto Fine Techno., Co. (currently in use for PCB mass production ,,, and especially in smartphones assembly). This buildup sheet consists of an epoxy–phenol matrix and spherical glass fillers.…”

Pulse Electrodeposition of Copper-Manganese Alloy for Application in Interconnect Metallization

“…In addition to its advantages for enabling 'seed-less' metallization of doped copper, a Cu-Mn electrodeposition process may also be applied to other integration schemes based on self-forming barriers 5 or for filling structures seeded with electroless Cu. 10 Electrodeposition of Cu-Mn alloy presents significant challenges associated with co-deposition of two metals with vastly different standard reduction potentials. 11 The standard reduction potential difference between Cu (E Cu = 0.34 V vs. SHE) and Mn (E Mn = -1.18 V vs. SHE) is 1.52 V. This large difference, coupled with excessive hydrogen evolution at potentials cathodic to the Mn deposition potential, presents significant challenges in achieving smooth and compositionally controlled Cu-Mn electrodeposits, as evidenced by previous attempts.…”

Electrochemical activation of substrate surfaces in microelectroforming

“…Applications for laminated microstructures fabricated with microelectforming exist in industrial products, such as multilayer microstructures, fuze safety devices, monolithic two-layer microstructures and metallic nanostamps [7][8][9][10][11][12]. Many researches indicate that the reliability of these microstructures is relevant to the adhesion strength between the electroforming layer and the substrate or the multi-electroforming layers [13][14][15]. Therefore improvement of the adhesion performance becomes an attractive research area in microelectroforming to enhance the reliability of the microstructures.…”