Printed Wiring Board Differential Pad Thickness for Warping
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Solution Overview
Problem
Existing printed wiring boards face challenges in achieving high connection reliability and preventing warping due to the thinness of wire-bonding pads, which can lead to faulty connections and increased electrical resistance.
Innovation Solution
A method for manufacturing printed wiring boards involving the formation of pads thicker than the conductive circuits, with a metal coating, to enhance connection reliability and reduce warping, by using multiple plating resist layers to control the thickness of the pads and circuits, and applying a solder-resist layer to expose the pads and circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the pad thickness is reduced to achieve thinner wiring, then the wiring density increases, but the connection reliability deteriorates and warping increases
Solution Approach 1:
The patent applies different thicknesses to different parts of the conductive structure: the pad region maintains greater thickness for reliability, while the wiring region uses thinner sections for density. This local differentiation resolves the contradiction by optimizing each region for its specific function.
Solution Approach 2:
The conductive structure is segmented into distinct functional zones: thicker pads for connection reliability and thinner wiring traces for density. This segmentation allows each part to be optimized independently, achieving both high wiring density and reliable connections.
2Quantity of substance
If the pad thickness is reduced to achieve thinner wiring, then the wiring density increases, but the warping increases due to thermal stress
Solution Approach 1:
The pad regions are maintained with greater thickness to provide thermal stability and resist warping, while wiring regions use thinner sections. This local quality differentiation ensures that critical connection areas have the thermal mass needed to resist warping while maintaining overall wiring density.
Solution Approach 2:
The conductive structure is segmented into thicker pad sections for thermal stability and thinner wiring sections for density. This segmentation allows the pad regions to act as thermal anchors that resist warping while the thinner wiring maintains high density.
3Reliability
If the pad thickness is increased to improve connection reliability, then the connection reliability improves, but the manufacturing complexity increases
Solution Approach 1:
The plating resist is applied in a preliminary action to define the pad regions before the plating process. This preliminary patterning allows the subsequent plating to automatically create the thickness variation, simplifying the overall manufacturing process while achieving the desired differential thickness.
Solution Approach 2:
The plating process itself generates the thickness variation through self-service: the plating resist pattern causes the plating solution to deposit metal at different rates or for different durations in pad versus wiring regions, automatically creating the required thickness differentiation without additional processing steps.
4Stability of the object's composition
If the pad thickness is increased to reduce warping, then the warping resistance improves, but the manufacturing complexity increases
Solution Approach 1:
The plating resist is applied in advance to define where thicker pads should form. This preliminary action enables the plating process to automatically create the thickness variation needed for warping resistance, avoiding complex post-processing steps while achieving the desired thermal stability.
Solution Approach 2:
The plating process self-generates the thickness variation required for warping resistance. The plating resist pattern causes differential metal deposition, automatically creating thicker pads that provide thermal stability and warping resistance without requiring additional manufacturing complexity.
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
The thicker pads increase the percentage of metal, reducing thermal stress and warping, while ensuring reliable connections by minimizing contact with the solder-resist layer and shortening connection wire length, thus enhancing connection reliability and reducing electrical resistance.
Implementation Method 1
forming a metal film on a surface of the insulative board
Implementation Method 2
forming a plating resist on the metal film
Implementation Method 3
forming a plated-metal film on the metal film left exposed by the plating resist
Implementation Method 4
etching to reduce the thickness of the plated-metal film exposed from the etching resist
Data Source
AI summary
A method for manufacturing a printed wiring board includes forming a metal film on a surface of an insulative board, a plating resist on the metal film, and a plated-metal film on the metal film exposed from the plating resist, covering a portion of the plated-metal film with an etching resist, etching to reduce thickness of the plated-metal film exposed from the etching resist, removing the etching and plating resists, and forming a wiring having a pad for wire-bonding an electrode of an electronic component and a conductive circuit thinner than the pad by removing the metal film exposed after the plating resist is removed, a solder-resist layer on the surface of the board and wiring, an opening in the layer exposing the pad and a portion of the circuit contiguous to the pad, and a metal coating on the pad and portion of the circuit exposed through the opening.