Although a standard PCB can also be differentiated from what an advanced PCB implies (Higher quality standards), the term includes different considerations that will be presented in this article in order to deepen the understanding of quality design for manufacturing. )Please note that this article will refer to units based on the International System of Units)
Why it is called standard PCB?
Have you ever designed a PCB but received comments that it cannot be produced unless some changes are done? This has to do with the fact that your partner’s manufacturing standards are not being met. Since 1957, the Institute for Printed Circuits has been collecting good practices as well as standardizing PCB design (IPC standards, which we will not cover in this article), including most important parameters for PCB design (size, holes, thickness, component placement…) to generate the concept of compliance.
While your PCB might not be a standard PCB in a whole (100% compliant), it is possible to undergo most of what a standard PCB defines to design accordingly, more on these considerations below.
A standard PCB will generally have three types of holes:
- PCB vias: They should all be the same size and generally it is recommended to use 0.6mm via holes with a 1.0mm copper pad, although 0.2 mm and 0.3 mm via hole size is suitable for higher density boards, when it is possible to avoid blind vias.
- Through hole technology (THT): This refers to the components that require this type of mounting on the board due to its packaging. Standard PCB holes are round, and it is recommended to have 1.0mm diameter holes. Take into consideration that most THT components have lead terminals from 0.8mm(passives, DIP), to 1.2mm (terminal blocks). It is better to follow the part manufacturer recommended hole size when a special hole design is required but will still be compliant with standard PCB design rules.
- Mounting holes: These are use for mechanical fixing of PCBs, and should comply with M type screws, please take a look at the common recommended sizes for standard PCB below:
Screw Recommended hole size
M1 0.75
M2 2.4
M3 3.4
M4 4.5
M5 5.5
M6 6.6
Please note that fiducial marks are used to help placement for the board during manufacturing process, but most recent machines are not requiring them anymore.
What is standard PCB hole size?
What is standard PCB thickness?
Depending on the number of layers the PCB will contain, the stack up preparation and impedance calculations will have to deduct the proportion of copper or prepreg that a specific layer must have. Nonetheless, most standard PCBs have an overall thickness of 1.6mm (1.57 considering what most manufacturers request and the Bakelite sheet standard thickness), but there is a range in these days that very from 0.78mm to 2.36mm (taking into account thickness tolerance) and this must do again, with the standard PCB requirements from the stack up but also related to the component density and the requirements to have smaller via holes on the board.
What is the standard PCB thickness tolerance?
As stated above, thickness must be met for standard PCBs depend on density and layers, but since the machine and manufacturing process is not 100% perfect, there is a tolerance for the overall thickness in a standard PCB, which is around ± 0.15 mm.
What are standard PCB card sizes?
What are the standards used in PCB design?
Previously, we defined that IPC Standards defined most of the norms for standard PCBs. The most related IPC standard for rigid PCB is IPC-6012C, which defines four classes of PCBs, six types (number of layers and vias) and three complexity levels (A, B and C, being C the most complex):
Standard PCBs for commercial use should be covered by the first two classes.
How many types of PCB materials are there?
Depending on the purpose of the electronic circuit, the dissipation of electronic waves and signal dissipation becomes critical, some other circuits must consider heat dissipation (e.g., lighting applications). However, a standard PCB will be formed by three raw materials:
- Resin: Must comply to the other two materials in terms of consistency and dielectric properties.
- Copper foil: It is cured with resin and conditioned to thermal requirements.
- Woven Glass Fabric: different width and thickness depending on the signal integrity requirements.
It is also important to remark aluminum as another material for standard PCBs. Just take into account that these standard PCBs are used for heat resistant applications.
What makes a good PCB design?
A good PCB layout design considers both physical phenomena and design standards, meaning that it will avoid most common problems on copper lines such as crosstalk and impedance mismatch, while conserving a good component placement and designation with most EMC/EMI compliance planned at the time of design.
It might take some iterations (board re-spin) sometimes to be fully compliant with a desired expectation but consider that good PCB designers start from the schematic and prototyping before deciding to go and manufacture a PCB. Practice makes perfect and this does apply to any discipline.
Conclusion
These notes provide a general understanding for standard PCB design and considerations. When designing a PCB, it is always important to talk and understand the standards and norms involved, in order to follow good design practices and avoid problems when sending your board for manufacturing! Hope that these details help in your further choices for your PCB design.
