Printed Wiring Board Solder-Resist Protrusion Design
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Solution Overview
Problem
The challenge in manufacturing printed wiring boards is the formation of small opening portions in solder-resist layers, which can lead to voids and reduced adhesiveness of solder bumps due to the fine pitch and diameter of bumps, and the need for improved adhesiveness and reliability in electronic component mounting.
Innovation Solution
A printed wiring board design featuring a solder-resist layer with a protruding portion that has a flat surface at its end, combined with a coating layer that covers and embeds the flat surface, enhancing adhesiveness and preventing recess formation, along with an adhesive layer made of a Sn and Cu metal layer and a silane coupling agent for improved bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If opening portions in solder-resist layer are made smaller to accommodate finer bump pitch, then productivity and miniaturization are improved, but voids form and adhesiveness of solder bumps deteriorates
Solution Approach 1:
A coating layer is formed on the pad surface before forming the solder bump, in advance preparing a reliable bonding interface. This preliminary coating prevents void formation and ensures good adhesiveness even when opening portions are small
Solution Approach 2:
The coating layer acts as an intermediary substance between the pad and the solder bump, mediating the bonding interface. This intermediate layer fills potential voids and enhances the adhesive connection between pad and bump
2Device complexity
If opening portions are made smaller for finer pitch, then device complexity is reduced, but manufacturing precision becomes more difficult to maintain
Solution Approach 1:
The coating layer is formed on the pad surface before subsequent processing steps. This preliminary coating provides a defined reference surface that helps maintain manufacturing precision even when dealing with small opening portions
Solution Approach 2:
The invention changes the surface parameters of the pad by adding a coating layer, which modifies the physical and chemical properties of the surface. This parameter change enables better control over the opening portion formation and solder bump adhesion
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design enhances the adhesiveness and reliability of solder bumps by preventing voids and improving the bonding between the solder-resist layer and the pad, ensuring reliable electronic component mounting with reduced transmission loss and increased frequency signal transmission.
Implementation Method 1
an adhesive layer made of a Sn and Cu metal layer and a silane coupling agent for improved bonding
Data Source
AI summary
A printed wiring board including an interlayer resin insulation layer, a pad formed on the interlayer resin insulation layer and for mounting an electronic component, a solder-resist layer formed on the interlayer resin insulation layer and the pad and having an opening portion over the pad, and a coating layer formed on the pad and exposed through the opening portion of the solder-resist layer. The solder-resist layer has a protruding portion protruding toward the inside of the opening portion in a bottom portion of the opening portion, and the protruding portion of the solder-resist layer has a flat surface in an end portion of the protruding portion.