IPC stands for Institute for Printed Circuits, currently known as Association Connecting Electronics Industries, found in 1975 for setting the standards for bare PCBs and finished PCB assemblies. The IPC classes for PCBs manufacturing are known as IPC Class-I, Class-II, Class-III and Class-III/A. It is obvious that class-I is the basic of PCB manufacturing quality and the Class-III/A the strictest. All three classes belong to the IPC-6011 standard. Major difference between classes is their level of qualification.
Below is a brief introduction to the different classes:
1.Class-I: Class-I PCBs are in the “Limited Life Expectancy” group or the electronics assemblies that are expected to be used in low reliability environment. These PCBs are used in the general electronic products, circuits and gadgets such as where the function of the product is sufficient to accept it. An LED light, flashlight, TV remote etc., are examples of Class-I PCBs.
2.Class-II: Class-II PCBs are in the “reliability products category” but reliability is not considered critical. These types of PCBs are used in dedicated products such as personal computers, laptops, tablets, smart phones etc.
3.Class-III: Class-III PCBs are highly reliable products and does not compromise over reliable operation of the product. The examples are electro-medical equipment, military equipment, electronic monitoring parts of automotives etc.
4.Class-III/A: This is another type of PCBs for which the manufacturing and inspection criteria are strictest. Their main applications are aerospace, military airborne systems and missile systems.
These classes actually define the level of inspection and acceptance of the user. In general the manufacturing requirements of all the PCBs are approximately same but require tighter tolerances for inspection that eventually result to enhanced product reliability. The parameters are controlled throughout the manufacturing process and final inspection. The faults if occur in any of the produced item are ensured traceable and if noticed that PCB may be destroyed. This practice makes sure that all of the PCBs produced are ‘fault free’ and comply with the tolerances specified by the respective class.
Generally, any manufacture can claim that he makes PCBs of class-II or III but the coupons and the certificates provided for each PCB are verified by another third party laboratory that certifies the reality about claimed class. Because, to manufacture, qualify and certify the manufacturing of each PCB is the sole responsibility of the manufacturer so it is upon the manufacturer that he does manage to qualify each the PCB for respective class. Either he makes more than requested PCBs and destroys the unqualified PCBs or makes every product with controlling the features upto his maximum and class category.
Fig. 1:- Class-II vs Class-III PCBs:
Manufacturing and acceptance the annular ring in the PCB is highlighted
Fig. 2:- PCB inspection stage for class-II or class-III
Fig. 3:- A comparison and list of IPC Class-I, II and III manufactured PCBs Inspection parameters