How thick should a Printed Circuit Board (PCB) and what is the baseline or standard for it? What are some of the reasons influencing the importance of a circuit board’s thickness?
A thick board can offer a wide range of benefits, such as supporting the resistance and conductivity capabilities of the PCB. Everything you need to know about the standard thickness, the benefits of the same and some of the special considerations are discussed in this article.
What is PCB Thickness?
It refers to the toughness or higher elasticity of the Printed Circuit Board (PCB). This has become a standard practice among many circuit designers, as it helps to increase the board’s resistance to damages.
What is Standard PCB Thickness?
It refers to the baseline or minimum thickness of PCB. Without this, it might be impossible to gauge whether the board can comfortably withstand some of the things and exposures it could have been exposed to.
The standard thickness is 1.577, which is the same as 0.062 inches. The reasons for the adoption include:
- It is a historical standard size for circuit boards. It dates back to the days of Bakelite Sheets.
- This standard thickness is also used across different facets, especially in the electronics industry, where it is used for both consumer electronics and related products.
The Variations to Standard PCB Thickness
Despite the historical advantage and the widespread usage; the 1.57mm size is not the only one you can find out there. Today, different variants are in existence. Examples are:
- 3.17mm or 125 mils
- 2.36mm or 93 mils.
- 0.031 inches or 0.78mm
- 0.03 inches or 2.36mm
What is the PCB Thickness Tolerance?
The ideal tolerance is 10% for the base thickness of 1.57mm. The tolerance can also vary, depending on the applications, the types of circuit boards and a couple of other design and manufacture factors.
How to Determine the Thickness of PCB Layers
The layers of the circuit board also have a role to play towards the accurate measurement of the thickness. For context, the higher the number of layers used, the more difficult it becomes to get the right dimensions.
The layers of the PCB can range between 2 and 32. Out of this, the considerations for the thickness range from resistivity, conductivity and mechanical weight.
PCB Copper Thickness
The copper (material) used in the circuit board can also influence the thickness of the board. Mostly measured in ounces, the thickness of the copper ranges between 0.5 oz and 2 oz. it is also common to have the measurement ranging from 1 oz and 2 oz.
The Factors Influencing Thick PCB
A circuit board is not thickened without a purpose. Certain factors, parameters and considerations influence how thick the board becomes.
The following are some of the common factors, broken down based on the roles they play:
1. The Design Factors
How the PCB is designed can influence the outcome of the thickness. Here are examples of the design-centric factors:
2. Copper’s Thickness
Also called the copper weight, it refers to the relationship between the current passing through the board and its thickness.
Measured in ounces per square feet, the base copper thickness is between 1 oz and 2 oz (1.4 to 2.8 mils).
However, the thickness of the copper can be modified depending on the following factors:
- The addition of more copper, depending on the increased need to increase the current’s thickness.
- The layer of the PCB increases as the weight/thickness of the copper increases.
3. Signal Types
What types of signals do the circuit board carry? Variations in the signal influence the board’s thickness in the following ways:
- The type of required signals impact the types of materials the board uses.
- Depending on the materials, the board’s weight can increase, especially if more (thick) materials are used.
The types of circuit boards are also considered here. For example, the High-Density Interconnect (HDI) boards using complex signals often have thinner footprints, thanks to the combination of the following:
- Thin, high-performance materials.
- Laser microvias and;
- Thin traces.
On the other hand, the PCBs conveying high-power signals tend to be thicker, thanks to the following factors:
- These boards use wider traces.
- They also use thicker copper.
4. The Type of PCB Material
What type of material does the circuit board use? It plays an important role in the thickness. Worthy of mentioning is that the Flame Retardant 4 (FR-4) material is commonly used because of the flexibility and availability of the substrate in different thickness options. You can find the FR-4 materials ranging between 0.2mm and 3.2mm.
5. Size and Flexibility Concerns
The type of material used also has a hand in the outcome of the board’s weight. Worthy of mentioning is that the considerations are between the thinner and thicker boards, all based on the materials used.
The following are some of the discrepancies between the thick and thin circuit boards:
- Rugged vs. Thin: thin circuit boards, such as the ones using the flexible materials are flexible, but pose a risk of lacking structural integrity. On the other hand, the thick PCBs are rugged.
- Space Considerations: thin PCBs tend to take less real estate in the circuit board, because of the flexibility. The reversal is the case with the thick PCBs that take up a lot of spaces within the board’s real estate.
6. Vias’ Type
The footprint created by the vias also plays a part in how thick the PCB becomes. Via in-pad, through via, buried via, blind via, and micro via are the common types of vias.
Despite the fact that these vias help to fast-track the routing of traces through the boards; they can also impact the size. For example, it is better to use the micro vias for the HDI circuit boards and the PCBs with thinner footprint.
7. How Many Layers Does the PCB Have?
The numbers of layers used in the circuit board also impact how thick it becomes. The general rule is that multiple layers equal more weight. Therefore, a multilayered PCB tends to weigh more and be thicker than one that uses a single layer.
- A single-layer PCB weighs around 1.6mm, while the standard PCB thickness for 2 layers is higher.
- Ideally, the 2-layer, 4-layer and 6-layer circuit boards often fall within the ambient of the standard PCB thickness.
8. The Operating Environment
Circuit boards adapt differently, based on the environments they are exposed to. Some contexts are given below:
- Due to the less thermal stability, the thickest PCB is best used in low-current operating environments.
- Both the flexible circuit boards and the ones with a thinner footprint are not ideal for use in rugged operating environments.
The Manufacturing Factors Influencing PCB Thickness
The processes that go into the production of circuit boards also impact how weightier the circuit becomes.
These are some of the manufacture/production-centric factors influencing the board’s weight:
Depanelization Method for the PCB
Depanelization refers to the process of separating jointed PCBs into individual circuit boards. Depending on the type of board, different depanelization methods should be used.
- It is better to route the thinner PCBs, as a way of creating breakaway tabs.
- The scoring depanelization method can be used to separate the thick circuit boards.
The Drill Hole Manufacturing Process
This has to do with the relationship between the drilling process and the underlying factors for making such holes in the PCB.
These are some of the considerations:
- Aspect Ratio: this is the ratio or figure highlighting the difference between the drill hole diameter and the hole’s depth.
- The depth and diameter capabilities of the lasers and drilling machines also influence the hole-drilling manufacturing process.
Layer Stackup
How the layers stackup or are outline on the PCB? The PCB manufacturer should be able to create stackups of the layers, especially for the PCBs with thinner footprints.
End-Use Environment
Where will the thick PCB be exposed to or used at the end of the day? The rule of thumb is that the harsher the environment is, the higher the thickness of the circuit board should be.
A harsh PCB environment is underscored by the following:
- Vibration
- Higher temperature
- Humidity
If your PCB’s use case is required for any of those environments, it means that you need to fortify it with more layers. This makes the board thicker, weigh more and have enough coverings to bolster the durability and reliability.
The PCB Assembly Process
The completion of the circuit board production process is not deemed over if the components have not been assembled.
At this point, the processes that go into the Printed Circuit Board Assembly (PCBA) have a role to play in the thickness.
Here are some noteworthy considerations:
- The Wave Soldering process is best-suited for PCBs with thicker layers.
- Consider using the Reflow Soldering process for the thinner circuit board layers. Doing so helps to aid heat or thermal energy transfer in the PCB.
Conclusion
The thickness of copper layer in a PCB can increase the board’s weight. Therefore, you should explain your layer requirements to the PCB Contract Manufacturer (CM). We will take your requirements into considerations, as a way of ensuring that the capabilities of the materials match the final PCB design.
