PCB Manufacturing Tolerances:
As we all know, PCB tolerances exist in every aspect of PCB Fabrication. For the industrial production of PCB, IPC6012C and IPC600H has formulated a set of international standards, and also clearly stipulated 3 Classes of acceptance standards. Different Classes require different PCB tolerances, and the Class 3 products require the most stringent tolerances.Customers should choose the appropriate acceptance criteria for their products, rather than pursuing higher acceptance criteria. If customers demands a higher standard excessively, the cost of PCB manufacturing will be higher and the lead time will be longer.Therefore, JHDPCB conducts PCB inspection strictly according to IPC6012C Class2(up to Class 3) and IPC600H Class2(up to Class 3). Most products only need Class 2.
If the tolerance range is considered at the design stage, it is beneficial to the subsequent PCB manufacturing and product application. To help you understand the source of these manufacturing tolerances, we have created a series of information guides:
|Types of Holes||Tolerance|
|0.8mm < PTH≤6.20mm||±0.075mm|
|0.2mm < Press fit≤6.20mm||±0.05m|
In the pcb manufacturing process, the thickness of the finished PCB is affected by various factors, so the final thickness also has a tolerance. According to the different types of PCBs, we give some examples of factors that can affect the thickness of the PCB.
Effects on Multilayer PCBs：
For multi-layer boards, there are many factors that affect the final thickness of the PCB. Please check as follows:
- Laminate tolerances.
- Prepreg tolerances.
- Lamination process (bonding of layers).
- Type of buildup (number of cores, prepreg, etc.).
- Resin content of the prepreg.
- Pressure and heat control.
- Flow characteristics.
- Copper layout (balancing/distributing more copper in an area increases the PCB thickness in that area).
|Board thickness(mm)||Tolerance of single & double-layer board (mm)||Tolerance of multilayer board(mm)||Tolerance of HDI board(mm)|
Accuracy of layer-to-layer registration is an important part of the PCB manufacturing process, which typically involves:
- Pattern-to-pattern registration of inner cores (e.g. L2 to L3).
- Inner core to inner core.
- Outer pattern to inner core.
- Outer layer pattern to outer layer drill pattern.
Knowing and managing the processes that affect inter-layer registration accuracy, we are able to reduce them to a minimum. We use mechanical pins and fiducials in conjunction with an optical registration system to ensure registration is within allowable tolerances.
It is important to understand the factors that affect the accuracy of layer-to-layer registration so that we can compensate during production. With the realization of direct imaging (DI), especially for solder mask, we have improved the registration capability, which can reduce the minimum solder mask ring.
Line Width and Line Space are important because they define the current load, impedance, and electronic signal integrity of the PCB. Therefore, the selected line width depends on the actual function of the PCB. For example, high currents require wider line and bigger line space as normal signal positioning.The main factors affecting the line width and line space are listed below:
- Base Copper Thickness.
- Copper Balance.
- The Etching Process.
- Base copper thickness
Base Copper Thickness.
The laminate copper thickness will define the smallest possible value of line width and line space. The thicker the copper, the wider the minimum line width and line space must be.
The distribution of copper on a layer of a PCB determines the rate at which the copper is removed. Copper balance is important for the uniformed removal of the unwanted copper during the etching process. Uneven copper balance will results in the smaller areas of copper etching quicker than large areas.
The Etching Process.
Etching is a chemical process and relies on the right parameters to provide a balanced and even removal of the unwanted copper.
Base copper thickness.
The thickness of the copper is important to the function of the PCB, and usually higher currents require thicker copper.
As a high-quality PCB manufacturer, JHDPCB knows how to manage and compensate for the above factors. However, there will always be some unavoidable tolerance. According to IPC A-600, the acceptable tolerance for line width and line space is 20%.
The thickness of copper in each layer of a printed circuit board varies by material and manufacturing process.When we consider copper layer thickness on a PCB, we mean:
Laminate Base Copper – Thickness of copper received from our supplier.
Finished Copper – This is the final thickness of copper on the finished PCB.
IPC-4562 and IPC-A-600 define acceptable thicknesses and tolerances for base and finished copper
In short, there are several factors that affect the end copper thickness of a plated PCB, including:
- Base copper thickness tolerance up to -10%
- Selected starting laminate copper thickness
- Number of cleaning processes required (each process removes a small amount of copper)
- Copper balance for PCBs
- Plating Process Tolerances
- Plus other
Our goal is always to provide you with a PCB that is as close as possible to the required specification, always within the allowable tolerances specified by the IPC standard.