Internal PCB Copper Pad Solder Mask for Reliable Via Lamination
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Solution Overview
Problem
In multilayer printed circuit boards (PCBs), the lamination process can cause prepreg resin to flow between conductive paste and copper pads, preventing solid electrical connections due to the resin becoming an insulator after curing, leading to open or sub-optimal connections between stack-ups.
Innovation Solution
Applying a solder mask material to internal copper pads on the PCB stack-ups before lamination, which remains solid and prevents prepreg resin from forming an insulating barrier, ensuring conductive paste can sinter and establish a solid connection between copper pads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the lamination process is performed without solder mask on internal copper pads, then the manufacturing process is simpler and faster, but the prepreg resin flows between conductive paste and copper pads creating insulating barriers that prevent solid electrical connections
Solution Approach 1:
The solder mask is applied to internal copper pads before the lamination process, creating a protective barrier in advance that prevents prepreg resin from flowing between the conductive paste and copper pads during subsequent heating and pressing operations
Solution Approach 2:
The solder mask acts as an intermediary material between the prepreg resin and the copper pad, blocking the harmful interaction where resin would otherwise create insulating barriers that prevent electrical connection
2Strength
If the lamination temperature is increased to improve bonding strength, then the bonding between layers is stronger, but the prepreg resin melts and flows more readily into vias creating insulating barriers
Solution Approach 1:
The solder mask is applied in advance to counteract the harmful effect of resin flow before it occurs, allowing the lamination process to proceed at temperatures that achieve strong bonding without the resin creating insulating barriers in the vias
3Strength
If the lamination pressure is increased to improve contact between layers, then the bonding is more effective, but the prepreg resin is forced into vias more aggressively creating insulating barriers
Solution Approach 1:
The solder mask serves as a protective intermediary on the copper pad surface that prevents forced resin entry into vias under high pressure, allowing effective lamination bonding to occur without compromising electrical connection integrity
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 enhances the reliability of conductive contacts between stack-ups by preventing prepreg resin from obstructing the electrical connection, resulting in more reliable and solid connections during the lamination process.
Implementation Method 1
a solder mask material is applied to a copper pad on what will be an internal layer of the final PCB. This solder mask is cured and will not substantially melt or flow during later lamination
Implementation Method 2
The conductive paste is sintered during the lamination cycle to form a solid via
Data Source
AI summary
Embodiments and fabrication methods for a printed circuit board comprising two or more electrically conductive layers, including at least a first conductive layer opposing and adjacent to a second conductive layer. Also including one or more electrically non-conductive layers including at least a first non-conductive layer disposed between the first conductive layer and the second conductive layer. A first copper pad is included on the first conductive layer. A second copper pad is included on the second conductive layer. There is a conductive via extending through the first non-conductive layer and electrically connecting the first copper pad to the second copper pad and solder mask material on the first copper pad around the via.