Desmearing of FR4 Epoxy Resin Using NMP-Based Sweller

Abstract

Drilling plate-through holes in multilayered printed circuit boards usually leaves a smear of dielectric material on the conductive surfaces which needs to be removed prior to deposition of conductive material. Desmearing utilizes sweller solutions to enhance smear removal. This study investigated the effects of varying the concentration of n-methyl-2-pyrrolidinone-based (NMP-based) sweller, temperature, and application time on smear removal. Diffusion coefficients were computed from weight gain versus time data, then correlated with temperature using an Arrhenius-type equation. The degree of smear removal was determined by measuring the amount of polymer oxidized over time. From the weight loss versus time data, the desmearing conditions that yielded a maximum weight loss of 0.42 mg cm À2 smear (at constant oxidation conditions) were determined to be 75 vol.% sweller solution, 353.2 K, and 2 min treatment time. Changes in surface characteristics due to sweller treatment and subsequent smear removal were qualified by examining the surface morphology of the polymer by scanning electron microscopy (SEM), identifying changes in functional groups by Fourier-transform infrared (FTIR) spectroscopy, and measuring changes in contact angles.

Improvements of the Epoxy–Copper Adhesion for Microelectronic Applications

“…The first treatment causes the swelling of the polymer BU matrix. Sweller molecules, for example 2-(2-butoxyethoxy)­ethanol, diffuse into the epoxy matrix, creating hydrogen bonds in between these polymer chains. , As observed earlier by Schröer et al, the created hydrogen bonding leads to a spacing of the polymer chains and thus to the macroscopic swelling of the matrix . Siau and co-workers proposed that the sweller leads to bending of polymer segments at the surface, , yielding accumulation of dense polar group clusters, in agreement with atomic force microscopy (AFM) and X-ray photoemission spectroscopy (XPS) results .…”

“…Among the wet treatments, alkaline permanganate etching was developed during the 1980s; it is efficient and cheap and continues to be the most widely used desmear. Permanganate etching presents the advantages of being more environmental friendly than chromic acid etching, and it is readily applicable to a wide class of BU polymers and composites. ,− The permanganate desmear sequence consists of three successive baths in which the PCB are immersed: (1) sweller, (2) permanganate etching, and (3) reduction of manganese oxide, as shown in Scheme .…”

Enhancing peel strength between liquid crystal polymer and copper with plasma treatment, surface oxidation, and silane coating

“…16 Surface oxidation and etching with permanganate is also an effective process to strengthen the bonding force between copper and polymer for FPC manufacturing. 17,18 Adhesive laminate 19 is the most commonly used process in the industry to improve the bonding force between the substrate and copper, but it will lead to an increase in sample thickness. Fully inkjet-printing, 20 laser etching and welding process, 21 and other physical processes 22,23 to activate LCP are all capable of obtaining good bonding performance.…”