Molded Solder Mask on PCB Bottom Surface for Warpage Reduction
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Solution Overview
Problem
Conventional solder mask formation on PCBs results in inconsistent thickness and gaps between the solder mask and electrical contact pads, leading to poor electrical connections, delamination, and warpage issues due to the weight of the solder mask.
Innovation Solution
A method involving the encapsulation of the bottom surface of a PCB with a mold material using a mold tool to achieve a precise, preselected thickness of the solder mask, ensuring it is co-planar with the contact pads and eliminating gaps, utilizing materials like epoxy resin for the encapsulating compound.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional photolithographic solder mask is applied on top of electrical contact pads, then the solder mask provides coverage and protection, but the thickness becomes inconsistent and gaps form between the solder mask and contact pads
Solution Approach 1:
The patent replaces the photolithographic chemical process with a molding process. Instead of using photoresist, exposure, and development chemicals to form the solder mask, the invention uses a moldable encapsulating compound that is mechanically molded onto the PCB surface. This mechanical molding approach provides precise thickness control and eliminates gaps between the solder mask and contact pads, directly resolving the inconsistency and reliability issues.
Solution Approach 2:
The patent changes the physical and chemical parameters of the solder mask material. Instead of using traditional photoresist with specific photopolymerization properties, the invention employs an encapsulating mold compound with different flow, curing, and adhesion characteristics. This parameter change enables the material to be molded precisely around contact pads while maintaining consistent thickness and forming reliable electrical connections.
2Reliability
If the solder mask thickness is increased to ensure coverage, then better protection is achieved, but the PCB experiences warpage and drawbridge effects due to the additional weight
Solution Approach 1:
The molding process replaces the need for excessive solder mask thickness. By using mechanical molding to precisely form the solder mask at the exact thickness required for coverage, the invention eliminates the need to over-compensate with thicker material. This precise mechanical formation ensures adequate protection while maintaining the minimum necessary thickness, thereby preventing warpage and drawbridge effects.
3Ease of manufacture
If photolithographic methods are used to form the solder mask, then the process is well-established, but gaps form between the solder mask and contact pads leading to oxidation and electrical shorts
Solution Approach 1:
The patent replaces the multi-step photolithographic process with a single-step molding operation. The moldable encapsulating compound is applied and molded directly onto the PCB surface, conforming precisely to the contact pad geometry. This mechanical approach inherently fills gaps and ensures complete coverage, eliminating the gap formation problem that plagues photolithographic methods while maintaining manufacturing efficiency.
4Reliability
If the solder mask is made thicker to prevent gaps, then coverage is improved, but the solder mask becomes heavy and causes delamination and poor electrical connections
Solution Approach 1:
The molding process enables precise formation of the solder mask at optimal thickness without gaps. The encapsulating compound flows into and conforms to the exact geometry of the contact pads during molding, ensuring complete coverage at minimum necessary thickness. This eliminates the need to increase thickness for gap prevention, thereby maintaining PCB structural integrity and preventing delamination.
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 approach ensures precise thickness control, prevents overlap and gaps, reduces warpage by up to 15%, allows for smaller pitch between contact pads, and enhances the reliability of electrical connections without residue on the contact pads.
Implementation Method 1
A molding process is then used to mold the encapsulating mold material into a solder mask on the bottom surface of the PCB
Implementation Method 2
The cured encapsulating mold compound comprises a solder mask disposed in between and in contact with the side walls of the electrical contact pads
Data Source
AI summary
A process for forming an encapsulating mold compound into a molded solder mask on a bottom surface of a PCB is provided that allows the molded solder mask to have a very precise, preselected thickness, or height, while also ensuring that no gaps between the solder mask and side walls of the electrical contact pads exist. A circuit board and circuit board assembly that incorporate the molded solder mask are also provided. The molded solder mask is fabricated in such a way that overlap between the molded solder mask and the electrical contact pads and gaps between the molded solder mask and the side walls of the electrical contact pads are avoided. In addition, the molded solder mask allows the pitch between adjacent electrical contact pads to be greatly reduced compared to the pitch that is possible using a traditional solder mask formed by the traditional photolithographic approach.