Wiring Substrate Terminal Plating Control
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Solution Overview
Problem
Conventional wiring substrates face challenges in reducing the pitch of connection terminals while maintaining reliable solder bonding performance, as electroless nickel plating can protrude and cause short-circuiting, and methods to prevent this often degrade bonding reliability or film quality.
Innovation Solution
A wiring substrate design featuring a metal layer inactive to the surface plating material, with a surface plating layer that covers the metal post's upper and side surfaces, and an exposed upper surface edge part, preventing the surface plating layer from protruding between adjacent terminals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electroless nickel plating is performed on the exposed connection terminal, then solder wettability is improved, but the plating protrudes to the area between adjacent connection terminals and causes short-circuiting
Solution Approach 1:
A barrier layer is introduced as an intermediary between the connection terminal and the surface plating layer. This barrier layer prevents the electroless nickel plating from protruding to the area between adjacent connection terminals, thereby eliminating the short-circuiting problem while still allowing the surface plating layer to provide solder wettability on the exposed connection terminal surface.
Solution Approach 2:
The surface plating layer is segmented into two distinct regions: a first surface plating layer on the exposed connection terminal surface that provides solder wettability, and a second surface plating layer on the barrier layer that prevents plating protrusion. This segmentation allows the plating to be controlled within specific areas and prevents harmful protrusion between terminals.
2Productivity
If the pitch of connection terminals is reduced, then device size is reduced, but electroless nickel plating protrusion more easily causes short-circuiting between adjacent terminals
Solution Approach 1:
The barrier layer serves as a mediator that confines the electroless nickel plating to specific areas, preventing it from protruding between adjacent connection terminals. This allows the pitch between terminals to be reduced without increasing the risk of short-circuiting, as the barrier layer actively prevents plating from extending into the spaces between closely-spaced terminals.
Solution Approach 2:
The barrier layer is formed in advance before the electroless nickel plating process. This preliminary action creates a pre-defined boundary that controls where the plating will occur, ensuring that even when terminals are closely spaced, the plating remains confined and does not cause short-circuiting.
3Ease of manufacture
If solder is applied only to the connection terminal of the semiconductor chip, then the connection terminal of the wiring substrate becomes recessed relative to the solder resist layer surface, but bonding becomes difficult
Solution Approach 1:
The connection terminal is given a three-dimensional structure with a metal post that protrudes from the insulating layer surface. This dimensional change ensures that the bonding surface is elevated and accessible, allowing solder to be applied to the chip terminal and bond effectively to the wiring substrate terminal without the substrate terminal being recessed and difficult to access.
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 allows for reduced pitch of connection terminals without short-circuiting, maintaining reliable solder bonding performance by restraining the surface plating layer's deposition and preventing it from extending to adjacent terminals.
Implementation Method 1
A surface plating layer may be formed by performing an electroless nickel/gold plating process on a surface of the connection terminal of the wiring substrate
Data Source
AI summary
A wiring substrate includes an insulating layer, and a connection terminal formed on the insulating layer. The connection terminal includes a metal layer formed on the insulating layer and including an upper surface, a metal post formed on the upper surface of the metal layer and including upper and side surfaces, and a surface plating layer that covers the upper and side surfaces of the metal post. The metal layer includes a material that is inactive with respect to a material included in the surface plating layer. The metal layer has an upper surface edge part that is exposed at an outside from the side surface of the metal post in a plan view. The surface plating layer is formed to expose the upper surface edge part of the metal layer.