In this article, I'll discuss the limits on IPC-6012 Class 3 annular rings as these are a standard fabrication requirement for high-reliability rigid PCBs. In the newer IPC-6012 standards, breakout is allowed for all but class 3 products. In the IPC-2221 standards, annular rings are applied universally for Class 1-3 products. As long as the annular ring is sufficiently large, the drill hit will not be considered defective and the board will have passed inspection. However, the two are related designers need to place a sufficiently large pad size on the surface layer to ensure that the annular ring that is leftover during fabrication will be large enough. Under the IPC standards for rigid boards, we have several possible fabrication characteristics that could be considered defects in different types of boards (HDI, flex, etc.) annular rings are just one of many possible structural characteristics that could be considered defects.ĭesigners often conflate leftover annular ring and pad sizes, something for which I am guilty of. This leaves behind an annular ring, something which might be considered a defect in certain IPC product classes. It's quite clear that some of these vias are off-center, meaning the drill hit that created these vias was not dead-center in the receiving land. Take a look at the above image of a PCB layout, specifically the vias and drill holes poking through the silkscreen.
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