Printed Circuit Board plays a crucial role in supporting electronic components, making the consideration of PCB thickness a significant task during the design phase. The thickness not only impacts mechanical performance but also influences the layout of electronic components and overall design. Typically, PCB thickness options are customized based on specific project requirements and the capability of the manufacturer, with a close relationship to cost. In this article, TechSparks will provide a comprehensive guide to PCB thickness by delving into its composition, standard thickness, and factors to consider during the design process. Let’s get started!
Typical PCB Thickness
To achieve functionality and miniaturization, electronic devices have gradually adopted transistors and integrated circuits, leading to changes in the manufacturing methods of PCB. In the early stages of development, Bakelite was the primary material, with a typical single-layer PCB thickness of 1/16 inch, approximately equivalent to 1.57 millimeters. However, as materials evolved, Bakelite was replaced, and standards shifted. In PCB manufacturing, to account for manufacturing uncertainties, a certain deviation is usually allowed. According to GB/T 4722 (Chinese national standard), the common PCB thickness and tolerance standards are as follows:
| Thickness (mm) | General Tolerance (+/- mm) | Fine Tolerance (+/- mm) |
|---|---|---|
| 0.5 | / | +/-0.07 |
| 0.7 | +/-0.15 | +/-0.09 |
| 0.8 | +/-0.15 | +/-0.09 |
| 1.0 | +/-0.17 | +/-0.11 |
| 1.2 | +/-0.18 | +/-0.12 |
| 1.5 | +/-0.20 | +/-0.14 |
| 1.6 | +/-0.20 | +/-0.14 |
| 2.0 | +/-0.23 | +/-0.15 |
| 2.4 | +/-0.25 | +/-0.18 |
| 3.2 | +/-0.30 | +/-0.20 |
| 6.4 | +/-0.55 | +/-0.30 |
Composition of PCB Thickness
Copper Thickness
The connections between components on a PCB rely on traces, also known as circuit patterns, drawn on copper layers. During the process, excess portions of the copper foil are removed through chemical etching to create the final patterns. Copper thickness, measured in ounces (oz), is a common unit for quantifying the thickness, with 1 ounce approximately equal to 1.4 mils. The copper thickness is closely tied to the current-carrying capacity of the circuit. In standard applications, 1-3oz copper thickness is typically used. For high-power applications, additional thickness, known as heavy copper PCB, may be required. The definition of PCB layers is N-layer PCB, indicating the structure includes N copper layers. Therefore, copper thickness directly affects the overall circuit board thickness.
Substrate Thickness
The substrate, serving as the main body of the PCB, exists between two copper layers, providing sufficient mechanical performance. Increasing the thickness of the substrate is highly effective in preventing signal interference and short circuits while also offering enhanced mechanical strength and stability. Additionally, substrate thickness influences the manufacturing process, with thicker PCB often being more versatile. This allows for easier creation of structures such as V-grooves without concerns about the risk of breakage. Taking FR4 substrate as an example, its thickness typically ranges from 0.2 millimeters to 3.2 millimeters.
Pre-preg Thickness
Pre-preg, short for pre-impregnated, is a type of glass fiber material typically containing uncured resin. Pre-preg layers are commonly sandwiched between two copper foil layers and then pressed together at high temperatures and pressures. This process ensures complete resin curing, bonding all layers together to form the structure of the PCB. Common types of pre-preg and their thicknesses:
- 1080: Thickness approximately 75µm, post-pressing around 70µm. It is cost-effective and has a long storage life.
- 2116: Thickness approximately 120µm, post-pressing around 115µm. It offers a balanced cost for durable PCBs.
- 7628: Thickness approximately 190µm, post-pressing around 180µm. Despite being more expensive, it provides higher insulation performance and bonding strength.
Do We Need to Increase PCB Thickness
We have already discussed the benefits of increasing printed circuit board thickness, and it is essential to recognize the need to incur additional costs. Therefore, before designing, ask yourself if you truly need it:
Flexibility or Rigidity?
Thicker PCB can provide more physical protection, suitable for applications that require resistance to impact. Conversely, thinner PCB might be more suitable for occasions that demand flexibility and lightweight characteristics.
Which Type of Vias to Use?
For high-density circuits, microvias might be the ideal choice as they offer a higher connection density. Thicker PCB, on the other hand, can accommodate more buried vias, enhancing internal space utilization.
Operating Environment of the PCB:
If the equipment will operate in harsh environmental conditions, increasing PCB board thickness can contribute to improved durability and stability. The added thickness can provide additional protection against chemical corrosion, resistance to high temperatures, and reduced electromagnetic interference.
Does the Manufacturer Meet the Requirements?
While most manufacturers can meet the requirements of standard designs, for special needs, your choices may be limited. Therefore, TechSparks recommends pre-selecting some manufacturers as your backup options before starting the design to avoid unnecessary high costs due to limited choices.
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