Printed Wiring Board Metal Posts for Fine Pitch and Cu-Ni Adhesion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing printed wiring boards with solder bumps face challenges in allowing easy contact between two terminals for resistance measurement and have low adhesion between the Cu layer and Ni layer due to small solder bump diameters and cylindrical shapes.
Innovation Solution
A printed wiring board design featuring metal posts with lower portions embedded in a solder resist layer and upper portions exposed, where the diameter of the top portion is 0.8 to 0.9 times that of the lower portion, facilitating easy terminal contact and accurate resistance measurement, and a surface treatment layer for enhanced adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If solder bumps with small diameter and cylindrical shape are used, then fine pitch formation is achieved, but adhesion between Cu layer and Ni layer deteriorates and terminal contact for resistance measurement becomes difficult
Solution Approach 1:
The metal post structure implements local quality by having different diameters at different locations: the lower portion (embedded in solder resist layer) has a larger diameter for adhesion, while the upper portion (exposed for terminal contact) has a smaller diameter for fine pitch. This localized variation in geometry resolves the contradiction between adhesion requirement and fine pitch requirement.
Solution Approach 2:
The metal post is segmented into two distinct portions with different functions: the lower portion for embedding in solder resist layer and providing adhesion, and the upper portion for terminal contact. This segmentation allows each portion to be optimized for its specific function, resolving the contradiction between fine pitch formation and adhesion.
2Productivity
If solder bumps with small diameter and cylindrical shape are used, then fine pitch formation is achieved, but terminal contact for resistance measurement becomes difficult
Solution Approach 1:
The upper portion of the metal post is designed with a specific diameter range (0.8 to 0.9 times the lower portion diameter) that is large enough to facilitate easy terminal contact for resistance measurement, while the overall fine pitch structure is maintained through the embedded lower portion. This local quality adjustment resolves the contradiction between fine pitch formation and ease of terminal contact.
3Ease of operation
If metal posts with top portion diameter 0.8 to 0.9 times lower portion diameter are formed, then terminal contact for resistance measurement is facilitated, but manufacturing process complexity increases
Solution Approach 1:
The metal post structure is formed preliminarily with the correct diameter ratio during the plating process, before the solder resist layer is formed. This preliminary action ensures that when the solder resist layer is subsequently formed and thinned, the metal post already has the appropriate geometry for easy terminal contact, reducing the need for additional complex processing steps.
Solution Approach 2:
The manufacturing process utilizes parameter changes in the plating conditions to achieve the desired diameter ratio of the metal post. By controlling plating parameters (current density, plating time, electrolyte composition), the top portion diameter is precisely controlled to be 0.8 to 0.9 times the lower portion diameter, simplifying the overall manufacturing process while achieving the desired geometric outcome.
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
Enables easy contact between two terminals for accurate resistance measurement and improves adhesion between the Cu and Ni layers, allowing for finer pitch metal post formation.
Implementation Method 1
forming an electrolytic plating film on an electroless plating film exposed from a first plating resist layer
Implementation Method 2
forming via conductors in openings in the outermost resin insulating layer and that a conductor circuit is formed on a surface of the outermost resin insulating layer
Implementation Method 3
applying plating in the openings in the second plating resist layer such that metal posts are formed on the via conductors
Implementation Method 4
forming a solder resist layer on the outermost resin insulating layer such that the solder resist layer covers the conductor circuit and the metal posts
Implementation Method 5
applying first etching on the part of the electroless plating film exposed from the electrolytic plating film such that the part of the electroless plating film exposed from the electrolytic plating film is removed
Data Source
AI summary
A printed wiring board includes a resin insulating layer, via conductors formed in the resin insulating layer, metal posts formed on the via conductors, respectively, and a solder resist layer formed on the resin insulating layer such that the metal posts have lower portions embedded in the solder resist layer and upper portions exposed from the solder resist layer, respectively. The metal posts are formed such that each of the metal posts has a top portion having a diameter in a range of 0.8 to 0.9 times a diameter of a respective one of the lower portions of the metal posts.