Minimum line width is one of the first questions asked of PCB Depanelizer, nevertheless the answer rarely includes “depending on copper weight.” To simplify your design process and prevent problems during manufacturing, we are going to demonstrate how and why line width is dependent upon copper weight. This brief overview gives some near-universal rules for trace width versus copper weight, together with other important considerations when working with heavy copper.
During etching, copper traces are just protected from the top by either a dry film or even a tin plate, which means that as copper is etched away, the edges of your trace will also be etched (quite simply, etching is definitely an isotropic process). The two main main outcomes of the isotropic etching – first, thick copper requires wider trace and space, and second, traces finish with a trapezoidal shape.
The table specifies starting copper and assumes consumption of a pattern plating process, as is the situation with the majority of Inline PCB Router. With rare exception, finished copper is certainly one ounce higher than starting copper in the outer layers, while on inner layers, finished copper is equivalent to the starting copper.
Certainly, 1oz copper thickness is regarded as the common and standard copper weight. Simply because it often hits the Goldie Lock’s sweet spot of not too much or too little. 2oz copper thickness is frequently more than is needed, while costing significantly more, and .5oz copper may not be enough, especially for ground planes that must endure higher currents. Therefore, 1oz copper thickness if often the best selection for fitting your design and budgetary needs.
What if you want tighter trace and space? Typically, you are able to duplicate the layer that will require heavy copper, then cut the copper weight in half. Therefore, should you need 8 mil lines and 4oz copper, duplicating the layer and taking advantage of 2oz copper is the perfect alternative.
For starting copper weights of 5oz or greater, we also recommend doubling a layer as opposed to using thicker copper. The price and processing difficulty from the thicker copper implies that adding layers is less expensive than using the thick copper. Quite simply, a 2-layer, 6oz copper board is often more pricey compared to a 4-layer, 3oz copper board.
On outer layers, the two main additional things to consider for heavy copper. First and simplest is soldermask – when working with liquid soldermask, multiple coats must adequately protect heavy copper traces. This concern is mitigated by 3D printed soldermask, but that technology will not be offered at every facility or in every color.
Second, surface mount pads could be compromised by heavy copper. Your Gerber file specifies the trace width with the lower trace, but SMT happens on the top of the trace. With heavy copper, the top of the the SMT pad can be several mils thinner than designed, creating more challenging placement and potentially a weaker solder joint.
One of the more important calculations in high current applications is definitely the cross-sectional area of a trace. IPC 2152 shows (conservative) cross-sectional areas essential for particular amperages, but designers stay alone to calculate the region of the trapezoidal trace. Sure, the area of your trapezoid is h*(b1 b2)/2, h is 18dexgpky copper weight (in mils!) and b1 is clearly the trace width, but what is b2? Your PCB Depenling sales and planning departments knows exactly how much smaller the top of the trace is in comparison to the bottom, so make sure you ask them. Keep in mind that the main difference varies from manufacturer to manufacturer.
Cross-sectional area of a via emanates from knowing how much plating is incorporated in the via. With Class 2 plating, the via wall is 20 microns (.0008”) thick. With Class 3 plating, the via wall is 25 microns (.0010”) thick. Begin using these thicknesses and also the diameter of your respective via to calculate the cross sectional section of a via, bearing in mind that this cross section makes an annulus. Keep in mind that Class 3 plating is normally requested on Class 2 boards. Hole wall plating thicker than 25 microns is not difficult in low volumes, but is not appropriate for a production part. Duplicating vias is generally a better solution than overplating. Utilizing a conductive via fill helps only marginally. Via fill material is undoubtedly an epoxy, meaning that the present carrying capacity is not really as high as pure silver or copper.