As the platform that carries all the spare parts of the whole machine, the motherboard plays an important role in the PC. When building a DIY machine, in addition to parameters such as chipset, supported memory type, and network card speed, some high-end motherboards can also see descriptions such as "6/8-layer PCB" and "2oz" copper. Although everyone knows that the bigger these numbers are, the better, but many veteran DIY players may not be able to tell their specific meanings. In fact, these two indicators are like the skeleton and blood vessels of the motherboard, which directly determine the upper limit of performance and stability.
PCB: three-dimensional wiring blueprint of the motherboard circuit
The full name of PCB is printed circuit board. It usually uses FR-4 as the base material. It is composed of epoxy resin and fiberglass cloth. The surface is coated with copper foil lines to connect to various components. In electronic products, the simplest single-sided board (1 layer) has conductive lines on only one side, and is usually used in small-scale devices with simple functions (such as remote controls, electronic toys, etc.). There are lines on both sides of the double-sided panel (2 layers), which can realize basic cross wiring. It is usually used in home appliances, high-end power supplies and other equipment.
But for PC motherboards (specifically desktop motherboards here), 2-layer boards are not even qualified for entry-level products. This is not only because the scale of the circuit is not enough, but also because there is no independent power layer and ground layer, and high-frequency signals can easily interfere with each other. At this time, PCB began to introduce the concept of layer number. Simply put, it is the number of layers of conductive copper foil in the circuit board. Each layer is separated by FR-4 insulation material, and the upper and lower layers are connected through metal through holes. Different layer numbers correspond to completely different circuit complexities.
Nowadays, mainstream motherboards are multi-layer boards (4 layers and above), usually with a structure of "signal layer - ground layer - power layer - signal layer" (you can think of a durian layer cake). The independent signal layer is like a shield to isolate interference.
Mid- to high-end motherboards commonly use a 6-layer board structure. The additional signal layer can accommodate more component connections. The "3+1+3" symmetrical lamination structure avoids warping and also increases the mechanical strength and heat resistance of the motherboard. Servers or high-end PC motherboards will also use an 8-layer board design, with each layer having a clear division of labor to keep complex circuits organized.
Copper: the "carrying ruler" of current transmission
Copper naturally refers to the copper foil circuits on all levels of PCB, but the unit "OZ (Ounce)" can easily be misunderstood as weight. In fact, it is the industry standard for copper foil thickness: 1OZ refers to the thickness of 1 ounce of pure copper covering 1 square foot of area. After conversion, it is about 35 microns, which is almost the thickness of three hairs.
1OZ copper is often the standard configuration of ordinary PC motherboards (including notebook motherboards). According to the current carrying formula, a 2mm wide trace made of 1OZ copper can stably carry 2.1A current, fully meeting the needs of conventional signal transmission. Some ultra-thin boards or motherboards use 0.5OZ copper (about 17.5 microns) in the inner layer, which can save space and control costs. As long as the design is reasonable, it will not affect performance.
Thick copper of 2OZ and above is an "enhanced blood vessel" prepared for high-power equipment. The current carrying capacity of 2OZ copper (70 microns) is twice that of 1OZ, and the heat dissipation efficiency is also greatly improved. Therefore, this design is commonly used in high-end PC/server motherboards to meet the stable power supply needs of top CPUs. However, thick copper also has disadvantages. For example, it is more difficult and costly to etch circuits, and it also limits fine circuit design.
However, the number of layers and copper thickness of the motherboard are never designed in isolation, but are accurately matched according to the positioning of the device. For example, ordinary desktop motherboards are usually 4-6 layers with 1OZ copper, which not only meets daily office and gaming needs, but also has a controllable cost. High-end motherboards will use a combination of 6-layer board + 2OZ copper or even 8-layer board + 2OZ copper, which can not only ensure stable transmission of high-frequency signals, but also cope with the high current and heat dissipation pressure during overclocking.