Electroplated Solder Deposits for Void-Free Joints
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Solution Overview
Problem
Current methods for forming solder deposits on substrates, such as circuit boards, often result in voids during reflow operations, which reduce the mechanical stability and electrical conductivity of solder joints, especially when dealing with fine structures and small bump pitches.
Innovation Solution
An electroplating method using a tin or tin alloy to form uniform solder deposits on substrates, including those with blind micro vias, without leaving voids, by depositing a conductive seed layer, patterning a resist layer, and electroplating the solder material into the substrate's recesses, followed by removal of the seed and resist layers, and applying a solder resist layer to expose the solder material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional methods (stencil printing or electroless plating) are used to form solder deposits, then the process is simpler or can handle larger bump pitches, but voids are formed during reflow operations reducing mechanical stability and electrical conductivity
Solution Approach 1:
The patent changes the plating method from electroless plating to electroplating, and modifies plating parameters (current density, temperature, pH, additives) to achieve void-free solder deposits. The electroplating process with controlled parameters prevents void formation during reflow, resolving the contradiction between reliability and harmful voids.
Solution Approach 2:
The patent applies preliminary actions by forming a specific seed layer structure (copper layer with controlled thickness and morphology) before electroplating the solder material. This preliminary preparation ensures uniform nucleation and growth of solder deposits, preventing void formation during subsequent reflow operations.
2Area of moving object
If bump pitch is decreased below 0.15 millimeter for higher density, then packaging density improves, but stencil printing becomes infeasible
Solution Approach 1:
The patent replaces the mechanical stencil printing process with an electroplating process. Electroplating uses electrical fields instead of mechanical stencil contact, enabling precise deposition of solder material at sub-0.15mm bump pitches that are impossible to achieve with stencil printing.
Solution Approach 2:
The patent changes the manufacturing method from stencil printing to electroplating, and adjusts electroplating parameters (current density distribution, plating time, bath composition) to achieve uniform solder deposits at high densities with bump pitches below 0.15mm.
3Manufacturing precision
If multiple process steps are used to form solder deposits, then manufacturing precision may improve, but process complexity and time increase
Solution Approach 1:
The patent merges multiple process steps into a more integrated electroplating process. By combining seed layer formation, solder material deposition, and pattern definition into a coordinated electroplating sequence, the patent achieves uniform solder deposits while reducing overall process complexity compared to conventional multi-step approaches.
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 method achieves void-free solder joints with improved mechanical stability and electrical conductivity, suitable for fine structures and various dimensions, reducing the number of process steps and ensuring uniformity and applicability even at small bump pitches.
Implementation Method 1
a solder deposit layer consisting of tin or a tin alloy is deposited by electroplating into areas not protected by the patterned resist layer
Data Source
AI summary
Described is a method of forming a solder deposit on a substrate comprising the following steps i) provide a substrate that includes at least one inner contact area, ii) contact the entire substrate area including the at least one inner contact area with a solution suitable to provide a conductive layer on the substrate surface, iii) form a patterned resist layer, iv) electroplate a solder deposit layer containing a tin or tin alloy onto the inner contact area, v) remove the patterned resist layer, vi) form a solder resist layer having solder resist openings on the substrate surface.