Nowadays, heavy copper PCB (copper thickness >4oz) has become popular in PCB industry because it is suitable for high-voltage and high-power application, as most PCBs are manufactured just for low-voltage or low-power application with traces generally contain from 0.5oz to 3oz copper weight.
1/For weights greater than 4oz, it is generally recommended to double a layer rather than using thicker copper.
2/Due to the trapezoidal cross section resulted from the etching process, an SMT pad may be thinner than designed and this may lead to weak solder joints or difficult component placement. Also, the solder mask will require multiple coats in order to protect heavy copper traces.
3/Plating the circuit board with heavy copper circuit enables the board fabricator to enhance the amount of copper thickness via sidewalls. Generally, high-power circuits and control circuits were produced differently on separate boards. Use of heavy copper plating makes it possible to incorporate high-current circuits to comprehend to simple board structure.
4/Traditionally when PCB's are used in military applications the designer creates the high current circuits by adding duplicate layers of 3 or 4oz copper in parallel and crossing their fingers that the layers share the current evenly between them. In practice, the sharing is less than ideal so some layers tend to carry a higher percentage of the load and generate higher losses. Overall, the board normally runs hotter than estimated during the design.
5/Utilizing Heavy or EXTREME Copper in creating the high current circuits combined with thicker copper plating in the via and plated through holes will eliminate the need to add duplicate layers in parallel, thereby eliminating any concern of load sharing among multiple layers. Temperature rise due to losses in the boards can be calculated with greater certainty. The thick copper plating in the holes dramatically reduces failures associated with thermal stress. The result is a cooler running and more reliable PCBA.
The heavy copper feature is excellent in its way as it can be seamlessly connected to standard circuit board. These standard and heavy featured PCBs can be placed with little restriction provided the designer and the fabricator consider manufacturing tolerances prior to final design.