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Method for printed circuit board layer interconnects using copper via plugs

IP.com Disclosure Number: IPCOM000008245D
Publication Date: 2002-May-29
Document File: 8 page(s) / 121K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for printed circuit board (PCB) layer interconnects using copper via plugs. Benefits include improved reliability and reduction of defects.

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Method for printed circuit board layer interconnects using copper via plugs

Disclosed is a method for printed circuit board (PCB) layer interconnects using copper via plugs. Benefits include improved reliability and reduction of defects.

Background

              Many problems are associated with the conventional method of using plated vias to connect the different layers in a circuit board, including:

·        The conventional method of creating plated through-hole vias is the most time consuming and expensive part of the PCB fabrication process. Each via in the PCB must be drilled, electro-less plated, electrolytic plated, and then plugged and/or capped. Due to the small drill bit diameter required to drill the small via holes, many drill bits are broken and PCBs scrapped.

·        When vias are plugged with solder-resist material, some of the solder resist material does not fully cure (see Figures 1 and 2). When the printed circuit board is processed through a reflow oven, the uncured solder resist reacts and emits a gas. In the case of via-in-pad (VIP), the gas builds within the via until the solder on the pad cannot contain the gas. The via out-gasses, spraying the solder around the via and pad. This can cause insufficient solder joints or solder shorts between pads.

·        Another issue concerning via-in-pad (VIP) is insufficient solder joints (see Figures 1 and 2). When the solder paste on a VIP pad reflows, it can wick down into the via, robbing the pad of its solder. The result is an insufficient solder joint.

              Via-in-pad (VIP) occurs when a plated through hole is placed usually in the center of a surface mount pad, electrically connecting two separate layers in the printed circuit board.

              No conventional solution is 100% successful. The process for creating the vias is the most expensive and time-consuming part of the PCB fabrication process. Via out-gassing occurs and must be overcome for VIP to be enabled in the industry.

              Conventional plated through-hole vias can cause defects such as insufficient solder joints due to the vias robbing solder from the pads. Conventional methods of plugging or capping vias with solder resist material can still result in out-gassing due to uncured solder resist in the via.

General description

              The disclosed method includes the insertion of copper via plugs into the printed circuit board to replace the conventional method of creating plated vias to electrically connect different layers in a printed circuit board. The via plugs may be copper nails or wire.

The key elements of the method are:

·        Copper via plugs are inserted into the printed circuit board by shooting a copper wire through the printed circuit board (PCB), or the copper wire may have high-speed threading and be spun into the PCB.

·        Copper wire is cut flush with the PCB surface after insertion.

Advantages

              The technical advantages of the disclosed method include:

·        Process steps such as drilling and electro-less plating are eliminated, reducing manufacturing costs.

·        Fewer proc...