Fabric circuit board refers to the Printed Circuit Board (PCB) manufactured out of fiberglass. As one of the common materials, it allows for the flexibility and improved thermal conductivity of the circuit board.
In this article, we explain the concept of making fabric PCB, compare it to the other PCB materials and highlight some of the advantages.
What is a Glass PCB Board?
It refers to the circuit board manufactured using the fiberglass material. The use of this material is for a wide range of purposes, such as satisfying the industry standards, fitting the pricing requirements for PCBs and providing improved properties.
The Fabric Fabrication Process in Circuit Board
The fiberglass goes through some processes before it is readied for use in a PCB. Here are some of the things that go into the production:
Glass Interlacing
The first process is to weave (interlace) fibers of glass yarn, which are available in different thicknesses and densities. Note also that the weaving is done until the glass yarn takes the form of a “fabric-like (fiberglass) sheet.”
Impregnation
The next step is to impregnate the fiberglass with epoxy resin. This is done for two purposes. The first is to form the cured resin (core) and the uncured resin (material) for the PCB.
Top Considerations for the Glass Fabric PCB
Certain measures need to be in place, if you are to get value from your fabric circuit board. The following are some of the top considerations when weaving or interlacing the fibers of glass yarn together:
1. The Tight Considerations
How tight the fabric is should make the list. Ideally, there are two options here: loosely-weaved and tightly-weaved. The rule of thumb is that the tighter the fabric is, the more uniform the dielectric constant becomes.
Here are some of the details:
Loosely-Weaved Epoxy Fill
If the epoxy resin is loosely-weaved, it tends to trigger a lot of issues in the circuit board’s laminate. These issues range from inconsistencies in the dielectric constant, fluctuations in the impedance and signal propagation skew.
Tightly-Weaved Epoxy Fill
On the other hand, the tighter the weave’s netting, the higher the chances of obtaining a uniform dielectric constant.
2. Zig-Zag Trace Routing
There is a risk of deriving an adverse impact of the weave glass style, when the trace’s direction is routed across a weave of sparse weave glass style.
A better way to modify this is to use a “zig-zag trace routing” format. This provides for the angular routing of the trace relative to the strands of the fiberglass.
However, this is not entirely a remedy as it causes another issue – taking up more spaces on the PCB. When more board areas are taken up, the outcome would be triggering feasibility issues.
In light of this, it is best to use a medium-woven glass style, such as the 2116 glass style. This is a tightly-woven fiberglass material that helps to address the impedance issues for the high-speed trace layers.
3. Cost-Effective Compromises
While the tightly-woven material helps to reduce impedance issues; it also causes another issue. This type of fiberglass material is quite expensive.
To this end, it makes sense to go for a cost-effective variant, such as the 1080 and 106 glass styles. They provide for the optimization of the high-speed trace layers and lower-speed signal layers.
4. Use Spread-Glass Materials
You may also want to use the spread-glass materials, which aid the avoidance of inconsistencies in dielectric constants, especially for the ultra-high-speed transceiver signal board designs.
The Circuit Board Pattern Fabric Manufacturing Process
Your fabric PCB can be produced in real-time, if you follow the steps below:
1. Design the PCB
The first step is to use a Computer-Aided-Design (CAD) software to make the board’s design. Once this is completed, you have to convert it from a design to a PCB layout.
2. Prepare the Substrate
The substrate is prepared via the cutting and drilling of the board’s panel to the desired size and shape.
3. Layer the PCB
The layering process entails using a lamination procedure to add a layer of copper both to the top and bottom of the board’s substrate.
4. Drilling and Plating
The drilling of the board paves the way for the plating process. The drilling procedure requires the creation of holes for the PCB components. These holes will also be used as a medium of interconnecting the layers.
Once that process is complete, the plating process takes over. Copper is used to plait or cover the holes. This is a medium for creating the space for integrating the Thru-Hole (THT) components. The plaiting of the holes also helps to create the needed electrical connections between the PCB layers.
5. Solder Mask Application
A layer of solder mask is applied to the circuit board’s surface. The application serves two purposes:
- It creates openings for the components to be placed.
- Solder mask also helps to protect important PCB components, including the copper traces.
6. Silkscreen Printing
This is a method of highlighting, revealing or pinpointing the location of the parts on the PCB. Applying a silkscreen reveals the positions of the testing points, reference indicators, the PCB components and other relevant markings.
7. Testing the Board
The fabric PCB can now be subjected to a series of tests to validate the performance of the components.
What Forms of Fiberglass Exist?
Fiberglass, being the central material used for making fabric PCBs, has different forms. These forms include:
Fiberglass Cloth
This is the most relevant form of fiberglass. It includes glass fiber yarns. Despite the wide range of options, you can rely on the fiberglass cloth’s insulation capabilities.
Fiberglass Tape
This form of fiberglass comprises of glass fiber strands and is reputed for the excellent thermal insulation properties.
Fiberglass Rope
This form of fiberglass is best suited for the applications used for packing purposes. The fiberglass rope form is made of a braided yarn that is also composed of glass fibers.
The Different Types of Fiberglass
You can find the fiberglass grouped into different classes. Of course, these classes refer to the different properties of the fiberglass, as well as the typical applications or use cases.
Haven said that, here are some of the common types of fiberglass you can find out there:
A Glass
The components are 25% alkali and 72% silica. Commonly used for the window glass applications, the A Glass type is not entirely heat-resistant.
C Glass
The main components are sodium borosilicate and boron oxide. The properties include corrosion resistance and durability.
D Glass
Here is one of the most popular choices for Printed Circuit Board (PCB) designs. Featuring borosilicate-based fiberglass, the D Glass features improved electrical properties, low density and an impressive dielectric strength.
E Glass
This is the best option for the high-electrical-resistant applications. The E Glass is popular for the higher resistance to electrical current.
The major component is alumina-calcium borosilicate. Due to this, the E Glass is designated “Glass-Reinforced Plastic (GRP)” due to the ability to perform multiple tasks.
ECR Glass
Calcium alumino silicate is the major component here. The outstanding property is the excellent corrosion resistance. This comes in handy for the prevention of the material from corrosion agents.
Fabric Circuit Board Applications
Printed Circuit Boards (PCBs) made out of fiberglass tend to be used in a wide range of industries. The following are some of the supported use cases:
Automotive
The automobile industry benefits the most from fiberglass PCBs. These boards play a central role in the production of different components, which are, in turn, used with a wide range of automotive-related applications.
Consumer Electronics
Electronic devices used in the mainstream also benefit from the use of fiberglass for the design. The excellent electrical properties and outstanding mechanical capabilities make it ideal for use with specific consumer electronics, such as radios, computers and telephones.
Medical Devices
Medical devices and wearables are also configured with the fiberglass circuit boards. The dimensional stability and low-heat conductive capabilities are some of the reasons for the usage in this industry.
Aerospace and Defense
The aviation industry, military and paramilitary parastatals also benefit from the awesomeness of fabric PCBs. Of particular mention is the circuit’s Glass Reinforced Plastic (GRP), which makes it a great fit for specific aircraft applications, such as instrument boxes and storage bins.
Fabric Circuit Board vs. FR-4
The fiberglass material is a popular substrate for manufacturing different kinds of circuit boards, such as multilayer PCBs, rigid circuit boards, single-sided boards, high-frequency PCBs and double-sided circuit boards.
On the other hand, FR-4 is a glass-reinforced epoxy laminate sheet, based on the fiberglass material. Although it is often interchanged for fiberglass, it is quite different from it.
Here are some of the clear differences between the two:
1. Cost-Effectiveness
If you are working on a budget, using the FR-4 material is not an ideal option. Rather, go for the fiberglass substrate, which is more affordable than the former.
2. The Components
Although both fiberglass and FR-4 circuits are made from a resin binder and fiberglass fabric, the FR-4 has more properties. One of its outstanding properties is the use of a woven glass fabric, as compared to the fiberglass’ use of non-woven fiberglass fabric.
3. The Mainstream Usage
When it comes to the most-used fabric, the FR-4 material carries the show. Due to the reduced need for specialized manufacturing, the flame resistance and mainstream availability, the FR-4 substrate is now used across different consumer electronic products.
4. The Electrical Properties
Despite the fact that both the fiberglass and FR-4 materials have excellent electrical properties; the former has more to offer. In this regard, we consider its low dielectric constant – a property that makes it ideal for use with the high-frequency applications.
The Thermal Properties
This refers to the materials’ capability to withstand overt exposure to heat. It is better to go with the FR-4 materials, due to the fiberglass’ slightly higher thermal expansion coefficient. This is the reason why the material is susceptible to warping.
The Benefits of Working with a Circuit Board Design Fabric
Using a fabric-based material, such as fiberglass, for your PCB design, comes with a lot of benefits.
Here are some of the motivating factors for this decision:
Chemical Resistance
Fiberglass possesses top-notch chemical resistance, thanks to the capability of wading off the negative effects of chemicals.
However, you want to note that the material might be exposed to powerful alkaline compounds.
Impressive Strength
The impressive strength-to-weight ratio is also another upside. In this case, the substrate is best for the applications that require improved strength levels.
Dimensional Stability
Get you a PCB material that doesn’t contour inappropriately. That is one of the outstanding features of fiberglass. Irrespective of the type of temperature it is exposed to, it doesn’t contract, expand or change form in response to such temperatures and environments.
Electrical Properties
Applications requiring higher electrical insulation often use the fiberglass PCB material due to the exceptional strength and low dielectric constant.
Moisture Resistance
What happens when a PCB is exposed to (excessive) moisture environments? Often times, the moisture gets into the board and causes internal damages.
The exceptional moisture-resistance makes the fiberglass material a good fit for the applications that don’t need overt exposure to moisture. This is also the reason why you can use the material across different environments, such as damp environments.
Fire Resistance
How susceptible is the substrate to catching fire? Despite the fact that the FR-4 material has been designated for such applications; the fiberglass substrate also stands a chance. Here are some of the things to know about the fire resistance capabilities:
- The material has a higher degree of strength retention. This is put at the retention of up to 25% of the strength, irrespective of the exposure to up to 540-degree Celsius of temperatures.
- Fiberglass materials neither propagate fires nor burn when exposed to one of such.
- There is a higher chance that the material doesn’t bring forth smoke. This is largely attributed to the inorganic material content that doesn’t make a spontaneous ignition of flames, especially when subjected to heat.
Conclusion
Fabric circuit boards do not catch fire, ignite the same and they have excellent electrical and thermal properties. Contact us today to start discussions on how to optimize your circuit board design and fabrication.
