A board can have several faults in it and the IPC standards define the acceptable defects. Some defects might hamper the performance of the board, some are purely cosmetic imperfections and will have no impact on the board’s consistent performance.
When it comes to annular rings, the IPC standards define the position of the holes on a landing pad and the width of the outer ring after a hole is drilled on to it.
An annular ring breakout is a condition where a via/hole is not completely surrounded by land/copper. The conductor to land junction is the 90⁰ area positioned around the point of contact between the conductor and the land. This area is specifically considered for annular ring breakouts
Which class of board to choose? IPC class 2 or IPC class 3 standard? Does it really make any difference? Are manufacturers solely responsible for the board quality? Do designers play any role in it? If you have all these questions on your mind then this design guide will help you clear up that ambiguity. PCB designers often wonder about the differences between the IPC classes. It is always the end application of the product that determines the type of board to be used in that particular design.
When we talk about IPC classes, we are speaking about the level of inspection that defines the manufactured board’s precision and reliability. The three classes are categorized based on the criticality of the application, the tolerances to the harsh environment, and so on. In short, the three classes determine the quality of the board. With IPC class 3 being the highest in quality and class 1 being the lowest. The other important thing that we would like to state here is that we cannot explain just about IPC class 3 without understanding the other two classes. Hence, in this design guide, we mention class 1 and class 2 for your better understanding.
Sierra Circuits offers internal quality review systems that guarantee zero-defect boards. We also provide engineering support to verify if your design is IPC Class 3/A or mil-spec compliant.
The amount of barrel fill required for through-hole leads is 50% for class 2 and 75% for class 3. As it can be delicate to get the paste into small PTH, our advice is to design your PTH 15 mils over the diameter of the lead.
As a rule of thumb, the minimum PCB dielectric for class 2 and class 3 is 3.5 mils. However, it can also be as agreed between the designer and the supplier. Talk to your manufacturer to learn more.