Minimum line width is among the first questions asked of PCB Depanelizer, but the answer rarely includes “depending on copper weight.” To simplify your design process and get away from problems at the time of manufacturing, we will demonstrate how and why line width depends upon copper weight. This brief overview gives some near-universal rules for trace width versus copper weight, as well as other important considerations when utilizing heavy copper.
During etching, copper traces are only protected from the very best by either a dry film or a tin plate, which means as copper is etched away, the edges of the trace may also be etched (quite simply, etching is surely an isotropic process). There are two main outcomes of the isotropic etching – first, thick copper requires wider trace and space, and 2nd, traces finish by using a trapezoidal shape.
The table specifies starting copper and assumes utilization of a pattern plating process, as is the case with virtually all PCB Routing Equipment. With rare exception, finished copper is one ounce greater than starting copper on the outer layers, throughout inner layers, finished copper is equivalent to the starting copper.
Undoubtedly, 1oz copper thickness is considered the most common and standard copper weight. This is because it often hits the Goldie Lock’s sweet spot of not a lot of or not enough. 2oz copper thickness is usually more than is essential, while costing considerably more, and .5oz copper might not be enough, specifically ground planes that must endure higher currents. Therefore, 1oz copper thickness if most of the most ideal selection for fitting your design and budgetary needs.
What if you want tighter trace and space? Typically, it is possible to duplicate the layer which requires 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 greatest alternative.
For starting copper weights of 5oz or greater, we recommend doubling a layer rather than using thicker copper. The fee and processing difficulty of your thicker copper implies that adding layers is less expensive than making use of the thick copper. To put it differently, a 2-layer, 6oz copper board is generally more pricey when compared to a 4-layer, 3oz copper board.
On outer layers, there are two additional considerations for heavy copper. First and simplest is soldermask – when working with liquid soldermask, multiple coats must adequately protect heavy copper traces. This issue is mitigated by 3D printed soldermask, but that technology is just not offered by every facility or even in every color.
Second, surface mount pads might be compromised by heavy copper. Your Gerber file specifies the trace width at the lower trace, but SMT happens on top of the trace. With heavy copper, the top of the the SMT pad may be several mils thinner than designed, ultimately causing harder placement and potentially a weaker solder joint.
One of the most important calculations in high current applications is the cross-sectional part of a trace. IPC 2152 shows (conservative) cross-sectional areas essential for particular amperages, but designers stay alone to calculate the area of any trapezoidal trace. Sure, the spot of your trapezoid is h*(b1 b2)/2, h is 18dexgpky copper weight (in mils!) and b1 is clearly the trace width, but precisely what is b2? Your PCB Depenling sales and planning departments will be aware of just how much smaller the top of the trace is than the bottom, so make sure you inquire further. Note that the main difference varies from manufacturer to manufacturer.
Cross-sectional region of a via originates from discovering how much plating is with 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. Start using these thicknesses as well as the diameter of your own via to calculate the cross sectional area of a via, bearing in mind the cross section makes an annulus. Keep in mind that Class 3 plating is typically requested on Class 2 boards. Hole wall plating thicker than 25 microns will not be difficult in low volumes, but is not suitable for a production part. Duplicating vias is usually a better solution than overplating. Employing a conductive via fill helps only marginally. Via fill material is an epoxy, which means that the present carrying capacity is not as much as pure silver or copper.