Heavy Copper PCB Voids via Nonwoven Prepreg
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Solution Overview
Problem
Conventional methods for manufacturing multilayered PCBs with heavy copper layers are costly and prone to void formation during lamination, and existing solutions, such as epoxy printing and resin-coated copper, are not thermally stable or suitable for mass production.
Innovation Solution
The use of a prepreg with a nonwoven glass web substrate, which has a higher resin content ratio than glass fabric, is employed to fill the space between heavy copper layers, eliminating voids and reducing thermal deformation, and the process involves laminating copper clad layers with nonwoven glass web prepregs and glass fabric prepregs under high temperature and pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If heavy copper (at least 4 oz, thickness about 140 μm) is used to increase the sectional area of copper for high current applications, then the current carrying capacity is improved, but voids are formed between copper patterns during the lamination process
Solution Approach 1:
The invention divides the lamination process into multiple stages with different pressure applications. First, a preliminary lamination is performed at lower pressure to establish basic bonding, followed by a second lamination at higher pressure to compress and eliminate voids between the heavy copper patterns. This segmented approach allows the thick copper layers to be properly consolidated without causing defects.
Solution Approach 2:
The invention performs preliminary actions before the final lamination by pre-compressing the copper patterns and adjusting the lamination pressure sequence. The first lamination step prepares the structure by initial bonding, and then the second lamination step applies increased pressure to ensure complete void elimination. This preliminary preparation prevents void formation during the critical lamination process.
2Strength
If conventional glass fabric prepreg is used as substrate, then the structural strength is maintained, but the resin content ratio is insufficient to fill spaces between heavy copper patterns
Solution Approach 1:
The invention applies different prepreg types in different locations within the PCB structure. Conventional glass fabric prepreg is used in areas where structural strength is the primary requirement, while high resin content prepreg is specifically applied in regions adjacent to heavy copper patterns where void filling is critical. This localized quality adjustment optimizes both strength and void prevention without compromising overall structural integrity.
Solution Approach 2:
The invention uses a composite approach by combining two types of prepreg materials: conventional glass fabric prepreg for structural support and high resin content prepreg for void filling. This composite material strategy allows the PCB to simultaneously achieve both high structural strength and effective space filling between heavy copper patterns, resolving the contradiction between these two requirements.
3Manufacturing precision
If resin-coated copper (RCC) is used as buildup material to increase resin content ratio, then void filling is improved, but thermal stability and mechanical strength are reduced
Solution Approach 1:
The invention applies high resin content prepreg only in specific locations adjacent to heavy copper patterns where void filling is needed, rather than using it throughout the entire PCB structure. This localized application achieves effective void prevention while limiting the use of thermally less stable material to areas where it is most beneficial, preserving overall thermal stability in structural regions.
Solution Approach 2:
The invention changes the resin content parameter of the prepreg material specifically in regions where void filling is required, rather than uniformly changing the material properties throughout. By adjusting the resin content parameter locally in high-resin prepreg and maintaining conventional prepreg in structural areas, the invention achieves both void filling and thermal stability without the drawbacks of using RCC throughout.
4Manufacturing precision
If epoxy material is used to print stepped portions of copper, then void filling is achieved, but manufacturing cost increases and mass production is not suitable
Solution Approach 1:
The invention enables the lamination process itself to perform the void filling function through the natural flow and compression of high resin content prepreg material during pressing. The resin in the prepreg automatically fills the spaces between heavy copper patterns under pressure, eliminating the need for additional epoxy printing steps. This self-service approach integrates void filling into the standard lamination process, making it suitable for mass production without additional cost.
Solution Approach 2:
The invention merges the void filling function with the standard lamination process by using high resin content prepreg that naturally fills spaces during compression. This combines what would otherwise be separate operations (void filling and lamination) into a single integrated process, eliminating the need for additional epoxy printing steps and reducing manufacturing complexity and cost for mass production.
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 results in a cost-effective, thermally stable multilayered PCB with no voids, reduced surface deformation, and lower thermal deformation, making it suitable for mass production and high thermal resistance.
Implementation Method 1
a prepreg 20, which is obtained by impregnating a substrate with a resin, is compressed at high temperature and pressure in a lamination process so that the space between patterns is filled
Implementation Method 2
compressed at high temperature and pressure in a lamination process
Implementation Method 3
compressed at high temperature and pressure in a lamination process
Data Source
AI summary
Disclosed is a PCB having multiple layers of heavy copper. A prepreg having a nonwoven glass web substrate is used alone or together with another prepreg having a glass fabric substrate so that the space between heavy copper, which is comparable to a thick film, can be filled efficiently without creating voids. The PCB includes a copper clad laminate having first copper patterned on one surface or both surfaces of a core substrate; at least one first prepreg laminated on one surface or both surfaces of the copper clad laminate, nonwoven glass web being used as the substrate of the first prepreg; at least one second prepreg laminated on one surface or both surfaces of the first prepreg, glass fabric being used as a substrate of the second prepreg; and second copper laminated on one surface or both surfaces of the second prepreg.