Flexible PCB Through-Hole Crack Mitigation via Layered Encapsulation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Flexible printed circuits prone to cracking near plated through-holes due to stress concentrations and the inherent brittleness of electroplated copper, which is exacerbated by bending stress and the presence of solder mask and finish plating.
Innovation Solution
A flexible multilayered construction for the flexible printed circuit with a conductive trace and inner and outer conductive layers that circumscribe the through-hole, with plating limited to the region adjacent to the through-hole, eliminating the need for solder mask and reducing stress concentrations by encapsulating the trace within additional layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder mask and finish plating are applied to the flexible printed circuit, then the circuit provides necessary protection and conductivity, but stress concentrations occur at the through-hole regions leading to cracking
Solution Approach 1:
The invention removes the solder mask and finish plating from the through-hole region, extracting only the necessary conductive plating while eliminating the protective layers that cause stress concentration. This selective removal resolves the contradiction by eliminating the harmful stress concentration effect while maintaining the essential protective and conductive functions in other areas.
Solution Approach 2:
The invention applies different properties to different regions: the through-hole region has only conductive plating without solder mask or finish plating, while other regions maintain the full protective coating structure. This local differentiation resolves the contradiction by eliminating stress concentration at the critical through-hole area while preserving protection elsewhere.
2Reliability
If electroplated copper is used to plate the through-hole, then the through-hole receives necessary conductive coverage, but the grain structure of electroplated copper makes it more prone to cracking under bending stress
Solution Approach 1:
The invention removes the finish plating layer from the through-hole region, extracting only the essential conductive plating. This eliminates the additional brittle layer that exacerbates cracking while maintaining the necessary electrical conductivity through the conductive plating alone.
Solution Approach 2:
The invention changes the structural parameters of the through-hole region by reducing the number of plating layers from multiple layers (including finish plating) to just the conductive plating. This parameter change reduces the overall brittleness and improves resistance to bending stress while maintaining conductivity.
3Reliability
If a multilayered construction with extensive copper plating is used, then comprehensive conductivity and protection are achieved, but the complexity and susceptibility to cracking at through-holes increase
Solution Approach 1:
The invention removes unnecessary layers (solder mask and finish plating) from the through-hole region, simplifying the multilayered construction while maintaining the essential protective and conductive functions. This selective extraction reduces complexity without compromising overall reliability.
Solution Approach 2:
The invention segments the treatment of different regions: the through-hole region receives simplified plating without solder mask or finish plating, while other regions maintain the full multilayered protective structure. This segmentation reduces overall complexity by applying the simpler structure only where necessary.
Data Source
AI summary
Flexible fingers for flexible printed circuits improve the crack resistance of prior art designs. The crack resistance can be improved by encapsulating the trace inside additional layers such that the outer two layers include only the lands of the through-hole, and all other copper is etched away. The crack resistance can also be improved with strategically adding copper on layers other than the trace layer including attaching is to the land of the through-hole as a stub. These two designs can be combined to include a stub trace into a four-layered design.