What Is an Ultra-Thin PCB?
As the name suggests, extra or ultra-thin PCBs are circuit boards with a narrower thickness than regular boards. Manufacturers achieve this narrow board thickness by reducing the width of the board’s base material, surface treatment, and conductive copper layer. Similarly, assemblers must keep up with this design by mounting low-profile components on the surface. This PCB design is ideal for applications requiring miniaturization while maintaining high reliability.Types of Ultra-Thin PCBs
Three types of PCBs adopt this ultra-thin design.Ultra-Thin Rigid PCB
The thickness of this PCB makes it challenging to create a rigid structure. Therefore, manufacturers make them as packaging substrates for integrated circuits, which helps make the structure extremely thin. You can make 25-micron broad areas, 50 microns on vias, below 175 microns for pitches, and 100 microns for pad diameters.Ultra-Thin Flexible PCB
The ultra-thin PCB substrate material for this type must have flexible properties, and the typical ones include:- Thin conductive copper layers
- Polyimide
- Adhesive
Ultra-Thin Rigid-Flex PCB
These PCBs have some parts rigid and others flexible. They usually feature plated thru-holes stretching across the rigid and flexible sections, enabling electrical connections in the multi-layered structure.
A rigid-flex PCB with the connector on the rigid section
The rigid sections provide hard surfaces for mounting the chassis and electronic components, while the flexible parts enable bend-to-fit applications or create vibration-resistant zones.Advantages of Ultra-Thin PCBs
- Short assembly time: Ultra-thin circuit boards feature configured lines that save time when linking excess lines.
- Lightweight design: Thin boards have tiny vias and small via-hole aspect ratios, narrow copper layers, and small lines/spaces, resulting in a light structure.
- Compact structure: Eventually, the lightweight design minimizes the board’s volume, making it compact and easily portable
- Efficient heat dissipation: Heat flows out quickly through the thin layers.
- Low cost: Reduced material usage cuts costs.
LEDs mounted on a thin, flexible ultra-thin circuit board
Other benefits include good solderability and easy component assemblyDisadvantages of Ultra-Thin PCBs
This design is not without its drawbacks, which include:- Signal losses
- Complex manufacturing
- Fragility
- Difficult to do repairs
- Design limitations
- Challenging temperature/thermal management
- Limited size
Ultra-Thin PCB Common Applications
These boards have the following applications.- Metro coins
- TF cards
- SIM cards
- NFC technology
- GPS devices
- Wearables
- IoT devices
- Mobile phone chargers
- Barcode equipment
- Medical devices
- Sensor cards
- Contact smart cards
A phone SIM card
Factors To Consider When Manufacturing and Assembling Ultra-Thin PCBs
These factors are critical when manufacturing and assembling these ultra-thin circuit boards.Substrate Material
The substrate PCB material is the board’s core that holds the components and copper traces. Although you should use thinner substrate materials than the ones in regular circuit boards, they should be stiff enough to prevent flexing. However, bending should not be an issue if making a flexible board.
PCB materials in single, double, and multi-layer circuit boards
PET (polyethylene terephthalate), polyimide, and FR4 core materials are typical for this board construction.Copper Layer
The boards also have thinner copper foils than the ones in regular PCBs. Depending on the board applications, this layer’s thickness should range between 9 and 18 microns.Vias
Drilling vias is challenging in ultra-thin boards because it can weaken the substrate and copper layers. But you can’t do without them because they enable signal and power transmission between the copper layers.
PCB pads and vias under a microscope
Therefore, you should carefully place and size the vias. Also, the hole’s diameter must be as tiny as possible, and the via should be as close as possible to the electronic components.Component Placement
Component placement is critical because it determines the overall thickness of the board. So, you should only use surface-mount components that have a thin profile. And install them near the PCB surface.Trace Width/Spacing
Calculate and evaluate the width of the transmission lines accurately to ensure you install an etched copper foil thickness that can handle the required electrical current without overheating.
A flexible PCB (note the conductor trace width and spacing)
While at it, calculate the optimal trace spacing to prevent cross-talk or electromagnetic interference in different circuits.Solder Mask
This masking is critical in circuit boards because it protects copper pads and traces from oxidation. Since we are talking about ultra-thin PCBs, this layer should be as thin as possible to keep the board within the required parameters.Thermal Management
Electronic components don’t function optimally when under heat stress. They can even get damaged. So, it is essential to implement thermal management mechanisms in PCBs to prevent this shortcoming, and the ultra-thin type is no different. Although the thin nature of these boards simplifies heat dissipation, implementing the thermal management mechanisms is challenging. Heat dissipation requires cooling structures like thermal vias and heat sinks, which are challenging to install on the thin board.Flexibility
Flexibility might be essential in some applications, especially those with space limitations. In such a case, manufacture rigid-flex or flexible circuits without compromising the board’s structural integrity.
A flexible keyboard PCB
You’ll have to use flexible materials and arrange the components carefully on the surface.Manufacturing Process
Fabricating these boards is more complex and requires stringent measures than making regular-thickness PCBs. Plus, you must have specialized manufacturing tools, thin copper foils, and thin substrate materials to fabricate the structure. Some required tools include specialized via-hole drilling technologies that can handle photo-via, plasma, or laser drilling.Testing
Ultra-thin circuit boards require careful handling because they have delicate structures. So, you should be cautious when testing them to prevent manufacturer or assembler-related damages. The most effective way to go about this testing process is to purchase specialized testing equipment to handle these PCBs.Ultra-Thin PCB Quality Standards
These circuit boards must adhere to the following quality standards to guarantee performance, quality, and reliability.IPC-6013
This standard specifies the quality and performance of flexible and rigid-flex PCBs. Some flexible PCB specifications cover the ultra-thin type in the following areas.- Design
- Manufacturing
- Performance
- Testing
- Components
IPC-6012
If you recall the ultra-thin PCB types, there is a rigid ultra-thin board. The IPC-6012 specification covers the design, manufacturing, performance, testing, and component performance of non-flexible boards, which include the ultra-thin subcategory.IPC-A-600
This guideline defines the acceptance criteria for PCBs, creating a benchmark for manufacturers and buyers. Specifically, this standard lists the visual criteria for examining and assessing PCB quality (including ultra-thin types), such as their craftsmanship.ISO 9001
ISO 9001 lists the quality management standards for companies, including the ones that manufacture and assemble ultra-thin circuit boards. Therefore, this standard ensures these boards have a constant level of quality.
A set of ISO-certified badge stamps
RoHS
RoHS is an acronym for Restriction of Hazardous Substances Directive, an EU directive that forbids several hazardous materials in manufacturing electrical and electronic equipment. Ultra-thin PCBs fall squarely in this category, and adhering to these standards means the structure does not have harmful materials like Lead, cadmium, and mercury.UL Guidelines
UL (Underwriters Laboratory) is a third-party certification company that rigorously tests products and machines to meet the required performance, sustainability, and safety standards. Therefore, a UL-certified badge on an ultra-thin PCB gives you confidence in the product’s performance and reliability in the long run.REACH
REACH adds to the effectiveness of RoHS to ensure ultra-thin PCBs are free from harmful chemicals. The EU legislation is an acronym for Registration, Evaluation, Authorization, and Restriction of CHemicals. It guarantees the safe incorporation of harmful chemicals into products like ultra-thin PCBs.
Multiple quality standard certification standard badges, including REACH and RoHS
Compliance means these circuit boards have zero toxic substances that can endanger your health.