Heavy copper PCB is a circuit board with a copper thickness that is ≥ 3oz per sq. ft in its outer and inner layers. What makes a circuit board classified as a heavy copper PCB is its thicker plating. During the production of heavy copper PCB, copper thickness is enhanced through plated holes and sidewalls.
For instance, when a PCB has 2 ounces of copper per sq. ft thickness, it is a standard PCB. However, if it has more than 3oz of copper, it is a heavy copper PCB. Heavy copper PCB is considered a reliable wiring option. Heavy copper PCB is different from extreme copper PCB which features within 20 oz to 200 oz per sq. ft.
The extra copper thickness allows the board to conduct more current. Heavy copper PCB has strong mechanical power in the plated-through-holes and connector sites. This type of PCB is also known as thick copper PCB.
What does Heavy Copper PCB offer?
Heavy copper PCB has a lot to offer. It has got some unique features that make it an ideal option for high-end applications. Let’s discuss some of the benefits of this PCB;
Great thermal distribution: Due to its copper-plated vias, this PCB offers high thermal resistance. Heavy copper PCB are used in applications that demand high speed and high frequency. You can also use this PCB at harsh temperatures.
Mechanical strength: Heavy copper PCB feature great mechanical strength. When this PCB is used, it makes the electrical system durable and robust.
Good conductor: Heavy copper circuit boards are a good conductor. They are utilized in the production of electronics due to this feature. They help to link various boards together. These boards can transfer current.
Onboard heat sink: Heavy copper boards offer an onboard heat sink. With these boards, you can achieve effective heat sinks on mosaic surfaces.
Great dissipation factor: Heavy copper PCB are ideal for large components with a high loss of power. These PCBs prevent overheating from occurring in electrical systems. They dissipate excess heat effectively.
Supports exotic material: Heavy copper helps to protect and enhance exotic material. Exotic materials are sometimes used for designing electronic components. An extreme temperature may need an exotic material. Heavy copper boards end circuit failures because they use an exotic material to its full capabilities.
How is Heavy Copper PCB Fabricated?
For the fabrication of heavy copper PCB, plating or etching is often used. The main aim is to add copper thickness to sidewalls and plated holes. The methods used in fabricating heavy copper PCB aren’t far-fetched. Heavy copper PCBs need special etching and plating methods to ensure the extra thickness of copper.
Using the normal etching techniques for the fabrication of heavy copper PCBs isn’t ideal. Normal etching methods produce over-etched margins and edge lines that are uneven. PCB producers now use advanced etching and plating methods to achieve straight edges.
During the PCB fabrication process, heavy copper PCBs are electroplated. This will help thicken the walls of PTH on the PCB. With this technique, the layer count shrinks and the impedance distribution reduces. When PCBs are exposed to several cycles during the manufacturing process, the plated holes can become weak.
The fabrication of heavy copper PCBs has its limitations which include;
- The etching process increases the cost
- The etching process requires a huge amount of copper to be removed
- It is hard to fabricate finer lines and thick copper traces
- Heavy copper traces make the surface uneven
Methods for Fabricating Heavy PCBs
Manufacturers utilize different techniques for fabricating heavy copper PCBs.
Embedded copper method: This method fabricates heavy copper PCB using a flat surface. Here the heavy copper is inserted within the prepreg resin. The thickness of the resin determines the thickness of the copper.
For instance, the fabricator begins with a 6-mil laminate and a 1 0z copper clad. Then the copper clad is covered with a photoresist. After this, a 5-mil laser beam is used to cut the circuit pattern from the side of the laminate. The laser has to cut via the laminate to the copper foil. If the laser is controlled, the fabricator can prevent the copper foil from damage.
The fabricator positions the laminate into a plating tank to electroplate. The copper plating produces about 6 mil plating thickness after filling the laser cut groove on the laminate.
Blue bar method: The blue bar method involves inserting thick copper bars into circuit boards. This method saves the material and reduces the weight of the PCB. During the fabrication process, the resin flows into space within the copper traces, this helps to achieve an even top surface.
Fabricators must pay attention to the level of copper fill between inner layers when it comes to multilayer boards with heavy copper layers. Low levels of fill and low levels of resin can lead to resin hunger.
Heavy Copper PCB Capabilities
It is important to consider the capabilities of heavy copper PCB when using them for some applications. This type of PCB is more expensive to produce based on their requirements. A heavy copper PCB should have these capabilities;
- A minimum board size of 6mm by 6mm and a maximum board size of 457mm by 610mm
- Copper thickness is greater than 3oz for each square foot.
- A board thickness between 0.6mm and 6mm
- Maximum external layer copper weight should be 15oz
- Solder mask color should be either green, blue, red, black, white, purple, or yellow
- Silkscreen color is white, yellow, or black
- The surface finishing should be Immersion Gold, OSP, and HASL
- The finished thickness is between 0.020 inches and 0.275 inches
Difference between a Standard PCB and Thick Copper PCB
Standard PCBs can be produced with copper etching and plating processes. These PCBs are plated to add copper thickness to planes, traces, PTHs, and pads. The amount of copper used in the production of standard PCBs is 1oz. In the production of heavy copper PCB, the amount of copper used is greater than 3oz.
For standard circuit boards, copper etching and plating techniques are utilized. However, heavy copper PCBs are produced via differential etching and step platting. Standard PCBs perform lighter activities while heavy copper boards perform heavy duties.
Standard PCBs conduct lower current while heavy copper PCBs conduct higher current. Thick copper PCBs are ideal for high-end applications due to their efficient thermal distribution. Heavy copper PCBs have better mechanical strength than standard PCBs. Heavy copper circuit boards enhance the capability of the board in which they are utilized.
Other features that make thick copper PCBs different from other PCBs
Copper weight: This is the main distinguishing feature of heavy copper PCBs. Copper weight refers to the weight of the copper used in a square foot area. This weight is usually measured in ounces. It indicates the copper’s thickness on the layer.
Outer layers: These refer to the external copper layers of the board. Electronic components are usually bonded to the external layers. The external layers begin with copper foil which is coated with copper. This helps to increase the thickness. The copper weight of the external layers is preset for standard designs. Heavy copper PCB manufacturer can alter the weight and thickness of the copper to suit your requirement.
Inner layers: The dielectric thickness, as well as the copper mass of the internal layers, is predefined for the standard projects. However, the copper weight and thickness in these layers can be adjusted based on your needs.