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Method to Mitigate Hollow Filament Failures in PCBs

IP.com Disclosure Number: IPCOM000249306D
Publication Date: 2017-Feb-16
Document File: 1 page(s) / 65K

Publishing Venue

The IP.com Prior Art Database

Abstract

A method to mitigate hollow filament failures in printed circuit boards (PCBs) is disclosed.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 56% of the total text.

1

Method to Mitigate Hollow Filament Failures in PCBs

Disclosed is a method to mitigate hollow filament failures in printed circuit boards (PCBs)

In locations on printed circuit boards (PCB) where there are sources of copper, an electrical bias, glass fiber, and moisture, potential exists for the formation of a conductive anodic filament (CAF). CAF causes a number of reliability problems which leads to failures within circuit boards. Typically, CAF occurs at an interface where the glass fiber has de-laminated from the resin or where a hollow glass fiber extends into the plated through-hole (PTH) via fabrication process. This creates a path for water diffusion and subsequent copper precipitation leading to conductive filament formation. Any method or process that eliminates hollow filaments, or fills/plugs the filament ends, would be desirable to mitigate CAF failures. Hollow fibers (HFs) are always present in PCBs. Depending on the PCB supplier, the prevalence of HFs can be more or less exaggerated and the probability of failures associated with these HFs can pose a true reliability concern. The disclosed method addresses this issue by plugging the HFs post PTH drilling. Several embodiments of the disclosed method are described below.

1) Right after desmear, the board is immersed in a non-aqueous fluid. A vacuum is then pulled to remove air from the HFs and enable the fluid to penetrate the HFs. Surface tension and wicking will ensure penetration of the fluid at least part w...