In PCB manufacturing, design engineers often encounter material designations such as 7628, 1080, 2116, 3313, 106, and 1078. These numbers identify different specifications of electronic-grade fiberglass cloth used to manufacture copper-clad laminates and prepreg.
Although the designations look like dimensional values, they are not simply measurements of thickness, width, or weight. They are standardized product codes. Each code corresponds to a particular combination of fiberglass yarn, weaving process, fabric construction, thickness, and areal weight. Understanding these designations helps engineers select suitable laminate and prepreg materials for multilayer PCB construction.
Where Do the Fiberglass Cloth Designations Come From?
The designations 7628, 1080, 2116, 3313, 106, and 1078 originated from the IPC-EG-140 standard issued in the United States in April 1988. This standard classified electronic-grade fiberglass cloth into 33 specifications.
The numbers therefore function as standardized industry model codes rather than direct physical measurements. A code identifies a defined fabric structure. That structure affects the finished material's thickness, resin absorption, resin content, mechanical reinforcement, dielectric behavior, and suitability for different PCB constructions.
For engineers, the main value of this coding system is consistency. A laminate manufacturer, prepreg supplier, PCB fabricator, and electronics manufacturer can refer to the same fiberglass cloth designation and understand the general material category being discussed. The code does not replace the complete material datasheet, but it provides a common starting point for material selection and communication.
Why Are These Numbers Used?
Standardized Industry Communication
Electronic-grade fiberglass cloth is a fundamental reinforcement material in PCB manufacturing. Without a standardized classification system, every supplier could use a different naming method for similar fabrics, making material comparison and supply-chain coordination difficult.
Once the IPC designations became widely used, numbers such as 7628 and 1080 became common technical language throughout the PCB industry. They allow participants in the material chain to identify a general fabric category without describing the entire weaving structure each time.
This standardization is especially useful when a PCB contains multiple dielectric layers. The fabric type influences the thickness and resin distribution of the prepreg after lamination. Therefore, a clear fabric designation helps laminate suppliers and PCB manufacturers maintain more consistent stackup construction.
The Relationship Between the Code and Physical Properties
The model code itself does not directly equal a physical dimension. However, each code is associated with typical physical characteristics. In general, a larger, heavier fabric designation such as 7628 represents a thicker and coarser fiberglass cloth, while smaller designations such as 1080 and 106 represent thinner fabric structures.
| Fiberglass Cloth Designation | Typical Thickness or Description | Typical Areal Weight | Common Characteristics or Applications |
|---|---|---|---|
| 7628 | Approximately 0.173 mm | Approximately 204.4 g/m2 | Thick, strong fabric commonly used in standard multilayer boards and power boards |
| 2116 | Approximately 0.094 mm | Approximately 102 g/m2 | Medium-thickness fabric |
| 1080 | Approximately 0.053 mm | Approximately 46.8 g/m2 | Thin fabric used in fine-line and higher-density PCB constructions |
| 3313 | Intermediate specification | Not specified here | Generally positioned between 2116 and 1080 in the listed material range |
| 1078 | Thinner than 1080 in the listed classification | Not specified here | Used where a thinner dielectric construction is required |
| 106 | Ultra-thin fabric | Not specified here | Used in high-density PCB constructions |
The values in this table are representative characteristics associated with the listed material categories. Actual thickness after lamination depends on the prepreg construction, resin content, pressing conditions, copper distribution, and the surrounding stackup. For this reason, the fiberglass designation should not be treated as a guaranteed final dielectric thickness for every PCB design.
How Fabric Thickness Affects PCB Construction
Thicker fiberglass cloth provides greater mechanical reinforcement and generally supports thicker dielectric layers. This makes 7628 suitable for many conventional multilayer boards, power boards, and applications where mechanical strength and economical production are important.
Thinner cloths such as 2116 and 1080 allow the designer to build thinner dielectric layers and more compact multilayer structures. They are useful when the stackup requires finer vertical spacing, higher wiring density, or tighter control of the distance between copper layers.
Very thin fabrics such as 1078 and 106 are associated with high-density constructions, including HDI boards, smartphone boards, and server-related PCB applications. The source material describes these thin fabrics as relatively constrained in supply compared with commonly used thick fabrics. Their use requires close coordination among the PCB designer, laminate supplier, and fabricator because thin dielectric layers can be more sensitive to resin distribution, copper pattern density, and lamination conditions.
The statement that smaller numbers generally indicate finer and thinner fiberglass cloth is a useful industry rule of thumb, but it should not be used as a substitute for a supplier's datasheet. The code identifies a material family; the final electrical and mechanical behavior depends on the complete laminate or prepreg specification.
Relationship Between Fiberglass Cloth and Prepreg
In PCB manufacturing, fiberglass cloth is impregnated with resin to form prepreg, also known as PP or preimpregnated material. During lamination, the resin softens and flows before curing, bonding adjacent copper layers and filling the spaces around the fiberglass reinforcement.
The fiberglass designation directly affects the prepreg designation. For example, a material identified as 1080 RC 67% indicates that the prepreg uses 1080 fiberglass cloth and has a resin content of 67%. In this notation, 1080 identifies the reinforcement structure, while RC 67% identifies the resin proportion.
Both elements matter. The fiberglass cloth provides reinforcement and influences the basic fabric thickness. The resin content affects resin flow, final dielectric thickness, filling capability, and the relationship between the prepreg and the copper pattern during pressing. A prepreg model therefore cannot be selected by considering the fiberglass code alone.
When multiple prepreg sheets are combined, their individual fabric types and resin contents influence the final interlayer thickness. The actual result also depends on the copper area and distribution on the adjacent layers. Areas with dense copper and areas with limited copper can press differently because the available space for resin flow is not uniform.
Material Traceability Across the PCB Supply Chain
The standardized designations provide continuity from fiberglass production to final electronic assembly. A typical chain includes the fiberglass manufacturer, copper-clad laminate manufacturer, PCB fabricator, and end-equipment manufacturer.
At the fiberglass stage, the designation identifies the fabric construction. At the laminate and prepreg stage, it becomes part of the material model used for dielectric construction. At the PCB fabrication stage, the designation helps engineers interpret the stackup and select compatible pressing materials. At the product level, it supports material traceability and consistency between production lots.
This traceability is particularly important when a PCB design is transferred between suppliers. A designation such as 7628 or 1080 provides a common reference, while the complete material data remains necessary for controlling thickness, resin content, dielectric properties, and processing conditions.
Key Points for PCB Designers
- 7628, 2116, 1080, 3313, 1078, and 106 are standardized electronic-grade fiberglass cloth designations.
- The numbers are product codes, not direct values for thickness or areal weight.
- 7628 generally represents a thick, heavy fabric, while 1080 and 106 represent thinner fabric categories.
- Typical fabric thickness and areal weight vary by designation and should be verified against the supplier's technical data.
- The fiberglass designation directly affects the corresponding prepreg construction.
- A notation such as 1080 RC 67% combines the fiberglass cloth type with the resin content.
- Final laminated thickness depends on resin content, pressing conditions, copper distribution, and the complete stackup.
- These codes improve communication and material traceability throughout the PCB supply chain.
In practical terms, the designations can be viewed as a standardized vocabulary for PCB reinforcement materials. They do not provide every detail needed for a stackup calculation, but they quickly indicate whether a fabric is relatively thick, medium, thin, or ultra-thin. Correct interpretation of the code, followed by verification of the complete prepreg and laminate datasheet, helps engineers achieve the required PCB thickness, mechanical strength, layer spacing, and manufacturing consistency.
