HDI PCB’s microvia technology
What is HDI PCB
HDI is a rapidly developing technology in the PCB industry. Compared with the traditional PCB, HDI board has higher wiring density, finer pitch and line width, smaller vias and hole pads, and higher connection pad density. Generally, laser drilling technology is used to drill the smallest micro-holes, and HDI boards usually contain blind holes and/or buried holes (different from the through holes from the surface to the surface)
By using HDI technology, designers can choose to place more components on both sides of the board. Use reduced part size and pitch to achieve more input/output in a smaller geometric space. This means faster signal transmission and significantly reduced signal loss and signal delay. Compared with the traditional circuit board design, due to the tiny pads and fine pitch on the HDI board, the mounting of these components on the HDI board requires higher precision.
For example, HDI technology makes it possible to reduce an 8-layer through-hole PCB to a 4-layer HDI micro-via PCB. The wiring capacity of a well-designed 4-layer HDI board can meet or exceed the functions of a traditional 8-layer PCB
Although the micro-via process increases the cost of the board, the reasonable design of HDI boards is accompanied by a reduction in the number of layers, and the reduction of materials also reduces costs. Generally, HDI boards are more effective.
Why are micro holes
Reduce costs: Use cost-effective liquid epoxy to plug the micro-holes on the PCB layer. Do not use resin-coated copper foils that usually have limited hole filling capabilities for microvias. Thin copper foil can be used, so that it will not reduce the reliability of the PCB.
Wiring density: Controlling the copper thickness of the inner layer of the PCB can produce the thinnest wiring. After inserting the microvia, we place the microvia on the ring pad of the inner through hole. We need to ensure the flatness of the outer surface to allow processing of fine traces. We can place microvias directly on the traces so that they don’t need any pads on the bottom. All this increases the routing density on this layer.
Reliability: In order to plug the micropores, a plugging material specially selected by matching CTE or thermal expansion coefficient is used. This allows the inner layer to have through holes with wall thicknesses up to 25 microns. This not only improves the reliability of the inner vias, but also improves the overall reliability of the PCB even if the traces are very thin. Our reliability test shows that even if the circuit board has undergone 1000 thermal cycle tests from -50°C to +125°C, this blockage will not cause any cracks or defects in the through holes.
Advantages of micropores
Microporous and HDI technology enables OEMs to achieve smaller, lighter, flatter and more portable products. With the development of SMT component technology and the addition of new geometries, such as flip-chip and chip-scale packaging (the pitch is reduced to 0.5 mm or less), it is becoming increasingly impossible for traditional PCB technology to use such advanced components. wiring. Using HDI as a new PCB manufacturing process, designers can reduce the pad size to 200 microns (0.008 inches or 8 mils). However, it is not possible to use a mechanical drill to drill holes on these pads because the required hole size is 100 microns (0.004 inches or 4 mils). This is where the micro-hole technology comes in, because the laser can drill such small holes easily and economically. The pore size of the micropores is reduced, thereby eliminating a large number of fan phenomena of BGA components. In addition, the microvias can be placed directly on the pads, thereby increasing the wiring density. One of the direct advantages of using microvia technology is to reduce the total number of layers, effectively reducing the stacking height of the PCB, thereby reducing costs. There is no need to use buried vias that need to be plated. HDI PCBs with buried microvias are more cost-effective, because the microvias only need to be blocked with special-purpose materials.
Completion
The microvias in the inner layer of the PCB provide many advantages for PCB designers and manufacturers. POE has been able to significantly reduce manufacturing costs through the use of PCB microvia and HDI technology. This is especially important when the PCB has a large number of through holes.
