There is no denying the fact that Industry Standards are very important when it comes to ensuring quality of products. With PCBs, the importance of Industry standards becomes even more pronounced as they impact the success or failure of the final product.
As per IPC-6011, there are 3 classes of PCBs. Each class represents a general kind of board and also delineates the kind of defects. Here is a broad overview:
The 3 classes of PCB namely Class 1, 2 and 3 in that order allow for defects in decreasing order. While Class 1 permits the maximum amount of defects and therefore least reliability, Class 3 has rather rigorous requirements.
This class of PCBs finds use in general electronic products that are known for their ubiquitous use. These PCBs are not required to last a long time and as long as the product functions, cosmetic defects are allowed.
The degree of stringency increases in this class compared to Class 1, although some amount of defects is still permissible. The usage of this Class is found in a range of communication equipment where high-performance is required, however these are not being used for critical appliances.
Clearly the most stringent class, its usage is found in critical products such as military and aerospace products as well as in life support systems. This class of boards clearly then need to function seamlessly and reliability is an absolute non-negotiable aspect.
What do these classifications imply in PCB Manufacturing?
By and large the class definitions determine the number as well as the severity of defects that are permissible in the PCB. While a PCB Manufacturer will try and create reliable boards, it is imperative that you know which class you want the board to conform to, depending on your bespoke needs. You need to study your own requirements carefully. For example, if you are fine with a board that lasts for 3-5 years, you would want to opt for a class 2 board that could come at a lower cost than a stringent Class 3 board that would come at a higher cost. On the other hand, if you are looking for a board for a mission-critical product, there is no way you would settle for anything lower than Class 3, irrespective of its cost. It is also important to remember that all PCB Manufacturers USA, may not have the equipment needed to meet the requirements of a Class 3 board. If your requirement is for a class 3 board, you would need to go with a PCB Manufacturer that offers this facility.
Broad overview of the defect criterion in the different classes
The different classes of boards have different benchmarks when it comes to performance as well as cosmetic defects. Here are some parameters set by IPC for each of these classes. Some of these include:
Annular Rings– When it comes to annular rings, some of the standards that IPC has laid down, include those related to:
- How centered the hole is?
- What is the width of the ring around the hole?
When it is a Class 1 ring, 180-degree breakout is required, while for class 2 it is 90-degree. In case of Class 3, however the ring needs to measure a minimum of 0.050 mm around the hole.
Solder Joints- For Solder coverage for joints, class 1 has no specification, class 2, 180-degree and class 3 has 270-degree specification.
Component Misalignment- Tombstone is a common defect that SMT components face. IPC therefore has laid down guidelines for component overhang. While for Class 1 and 2, it is less than 50% of pad width while for class 3, it drops to 25% of pad width.
Selecting the right class for your board needs a careful analysis of the following:
- The requirements for each Class
- Your own design objectives
IPC’s guidelines, therefore, ensure that you are certain of the degree of dependability being offered by the board and that you are not found wanting on the reliability front. The fallouts of using a Class 1 board for a mission critical appliance can, as the above classifications suggest, be glaring.
It is important to choose the right PCB Manufacturer USA, to ensure that the required capability to deliver these boards is correctly met. A seasoned manufacturer would have the requisite experience in IPC PCB Manufacturing that will go a long way in ensuring reliability of your product.
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