Buried PCB Solder Pads for High-Density SMD Assembly
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Solution Overview
Problem
Existing methods for fixing surface-mounted components (SMDs) on printed circuit boards face limitations in increasing component density, lifespan, and mix of component types due to constraints in standoff height and solder paste application, particularly with fine-pitch and large components, leading to assembly difficulties and reduced assembly yield.
Innovation Solution
A method involving the formation of cavities in the conductive and insulating layers of a multilayer printed circuit board, filled with a metal alloy and solder flux, allowing for increased standoff and flexibility of solder joints, enabling diverse component placement without constraints on density or type.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the size of holes in the silkscreen is increased to increase solder joint height, then the standoff is improved, but the component placement density deteriorates
Solution Approach 1:
The patent applies local quality by creating cavities with varying depths at different locations on the printed circuit board. Specifically, first cavities are formed with a first depth to accommodate first surface-mount components, while second cavities are formed with a second depth (different from the first depth) to accommodate second surface-mount components. This allows each component type to have optimized standoff height locally, resolving the contradiction between achieving sufficient standoff and maintaining high component placement density.
2Ease of operation
If the screen thickness is reduced to accommodate fine-pitch components, then the fine-pitch component assembly is improved, but the solder paste volume deteriorates
Solution Approach 1:
The patent transitions from a two-dimensional surface soldering approach to a three-dimensional cavity-based approach. Instead of varying screen thickness in the Z-direction, the invention creates cavities with controlled depths in the vertical dimension, allowing solder paste to be contained and accumulated within these cavities. This dimensional change enables sufficient solder paste volume to be maintained while still accommodating fine-pitch components with precise placement requirements.
3Ease of manufacture
If the window area is increased to maintain screen removal ratio, then the screen can be removed without damage, but the fine-pitch component placement deteriorates
Solution Approach 1:
The patent segments the solder paste application areas by creating multiple discrete cavities across the printed circuit board. Each cavity acts as an independent containment zone for solder paste, allowing the silkscreen to have multiple small windows rather than requiring large continuous areas. This segmentation enables the screen removal ratio requirement to be met while maintaining small window sizes suitable for fine-pitch component placement.
4Reliability
If the solder paste volume is increased to ensure long lifespan for large components, then the reliability is improved, but the fine-pitch component soldering deteriorates
Solution Approach 1:
The patent applies local quality by providing different cavity depths for different component types. Large components are positioned over cavities with greater depths that contain increased solder paste volume for enhanced reliability and lifespan. Fine-pitch components are positioned over cavities with appropriate smaller depths that provide sufficient but controlled solder paste volume for precise soldering. This localized differentiation resolves the contradiction between ensuring long lifespan for large components and maintaining ease of operation for fine-pitch component soldering.
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
Enhances component density and lifespan while allowing for various component types, including fine-pitch and large components, with improved assembly yield and reduced manufacturing complexity.
Implementation Method 1
the heat remelts the alloy and evaporates the solder flux, forming solder joints from the metal alloy in the solder paste
Implementation Method 2
the heat remelts the alloy and evaporates the solder flux
Implementation Method 3
the bare printed circuit board is first screen-printed by covering the conductive layers (usually copper) with solder paste using a screen printing stencil
Implementation Method 4
the height of the solder joint is increased by coalescence: the thickness of the solder joint is greater than the equivalent thickness of alloy obtained after reflow with smaller holes in the silkscreen, since the metal alloy cannot spread beyond the printed circuit board layers
Implementation Method 5
In use, the SMD and the surface to which it is soldered expand and contract differently, causing relative displacements, particularly in the plane of the surface (X, Y)
Data Source
Figure 1a~1c
Figure 1d~1f
Figure 1g~1i
AI summary
The invention relates to a method (S) for manufacturing an electronic board (1) comprising the following steps: - forming (S1, S4) a cavity (20) in the conductive skin layer (Ci) and in an underlying insulating layer (10), such that at least a portion of a solder pad (4) is exposed, - filling (S5) the cavity (20) with a solder paste (24), - positioning (S6) an SMD (3) opposite the cavity (20), - and soldering the SMD (3) on the electronic board (1).