About Trace Width and Tolerance
As is well-known, the printed circuit board (PCB) not only mechanically supports but also electrically connects electronic components . So the trace in PCB plays a vital part and decides whether the function of the finished PCB is well or not. Actually, there exist several important points about the trace and to which you’d better pay some attention. Now let’s begin with the basic knowledge of trace width and tolerance.
Trace width
Trace width is the first thing you need to attach great importance. In the PCB fabrication process, the smaller trace widths are, the more difficult to be etched again and again. For this reason, manufacturers always limit how small a trace will be, by which they can control the trace width and undertake the process of repeated etch. Considering the influence of etching back, manufacturers will increase the trace width and pad diameter on the film so the board will finish at required width. However, this increase should be based on the minimum spacing requirement, and if the clearing requirement is followed, the minimum trace width remains the same regardless of the copper thickness. Generally speaking, the minimum trace width is .006’’ (+/-.001) [.1524(.0254)], but manufacturer may adjust the manufacturing process and document according to the possible changes.
Trace tolerance
Since different manufacturers use different technologies, it results with different etch-back allowances and trace tolerance. Provided that the tolerance is not defined in the board, then the manufacturer will decide the tolerance. Default tolerance (for most manufacturers) for trace and space is .002’’ [.0508]. This is the recommended tolerance value, but +/-001’’ [.0254] tolerance may be used if required tightly.
