The current board interconnect technology and compared the situation a few years ago can be found, although significantly improve product performance, but the cost and no corresponding increase was mainly due to new materials and new device makes the emergence of interconnection technology made considerable progress , Such as surface array packages such as BGA and CSP; for flip-chip, micro-through hole in the PCB on the development of a breakthrough, but also makes small package of close to the limit. In this paper, multi-layer circuit boards in the micro-hole production process, to discuss how to achieve high-density circuit board wiring.

     The first generation of micro-hole PCB in the market was a huge success, to the millions of sales, the facts also prove that this is an effective and reliable technology. As micro-hole PCB has higher performance and lower cost, estimated in recent years, the market will develop rapidly. Micro-hole technology has also continued progress, structural transformation greatly enhanced the integration, especially at the same time both sides have a number of micro-hole of the PCB is even more substantial increase interconnection density.

     Micro-hole is less than 0.15 mm in diameter hole, it is the machinery of the drilling area of approximately 1 / 4. As a blind hole, they only have to connect to the story line there, help to achieve a higher density interconnection. Micro-hole forming laser completed, its speed much faster than mechanical drilling, and cost much lower than the latter, its main advantages to these applications not only confined to the outer line. Despite the reduced size of the existing hole can also achieve high-density interconnection, but with the design requirements increasing, PCB costs will continue to rise, transforming the existing process than to switch to a brand-new technology costs more Lower, such as the use of 2 + n + 2 plot structure.


     In recent years mobile communication products have become much more complex than cellular phones, such as portable satellite phones, personal intelligent communications, electronic notebook and video signal processing applications, these products have in common is the interconnection and the very high density High-frequency aspects of special requirements. They surface most of the board room full of many small space components, in the most outside of the first layer and m-(m representative of the total number of layers) has basically no place can be used for wiring, which can only be, Layer, such as the second layer and m-1 layer. 1 + n +1 in the structure, these include some of the drilling machinery from a larger electrical conductivity of copper connected to the inner ring and used, may not be able to provide adequate space for high-density wiring. A solution is to make the second layer and m-1-a-hole layer, a layer under it in connection with the reduced area occupied, so you can go online. The usual practice is to make as much as possible with the density of interconnection components close, it is necessary to achieve this is the best use of micro-hole, if necessary, should also use multiple-hole layer.

     The first 2 + n +2 structure of circuit boards use only direct link with the adjacent layer of micro-hole, the basic production method is to make a micro-hole of the steps to repeat. Figure 1 is to use staggered with the first tier and third tier-through hole through the connection diagram. This 2 + n +2 structure of the use of resin-coated copper (RCC) technology production, particularly worth mentioning that the method can guarantee that all have a very high level of the coplanarity. This structure can take many forms (Figure 2).



     Micro-hole production cost is a major hole forming and electroplating. For some applications, can reduce both the process of cost reduction, for example, in the second and third tier or m-1 layer and m-2-on-between if there is no hole, there was no need for the relevant Electroplating process, available at this time other types of micro-Hole replace the hole. Also available through micro-hole PCB will be the third of the surface layer and a direct connection (Figure 2 a), through holes 1-3 will be connected to the outer layer and the third, and then through holes 1-2-3 and the second layer connected ( Figure 2 b), through this method can achieve all the necessary interconnection.

     In general, to ensure reliable through hole plating, through hole through holes 1-2-3 and 1-3 in diameter must be greater than in neighboring only link between the two hole. If not through holes 2-3, it will only be realized through the first tier of the second and third tier of connectivity, this would cause a waste of space for the first layer, the overall final interconnection will be lower than the density of a map showing Situation. However, there are no hole to 2-3 in the second layer on the production of fine lines, because only the RCC copper foil for the primary copper etching, it can be very high resolution graphics.

     - Hole 1-3 mask the use of shape-generation technology, the first film in the RCC copper etching of a mouth, and then use infrared laser ablation swap resin, the productivity of these two are very high. Etching is a parallel process, laser ablation resin only bored, you can use fast CO2 laser. 1-3---there are still some interesting applications, such as the structure's second floor and potential of m-1 has remained unchanged, as a shield, lining between them and without any connections, it Do not need to layer 2-3 hole, in this particular to electromagnetic compatibility (EMC) demanding occasions, in the lining on the wiring.

     Production of the 1-2-3 hole, the second-tier general Futong by UV laser hole, bored of this slow, if you use shape-mask process, you need the larger hole ring. Figure 3 compares the first tier and third tier connected several ways, usually with staggered-hole is the most popular method, in exceptional circumstances, the hole 1-3 and 1-2-3 occupy more space - Is acceptable, and the use of shape-mask process will be a greater waste of space.

Micro-hole on -

     Micro-and micro-through hole through holes between the lines of the micro-is to produce multi-layer circuit boards through hole of the key. Under normal conditions of micro-hole on its lower deck of a digital circuit, this approach will enable the smallest micro-hole pad save space and take full advantage of the benefits, but it is the other bit of bad for the price. With the increasing number of layers PCB, the error will be more and more, but as long as there is no element at the same time and required to have at all layers, the accumulation of such deviations will not cause any problems, it should be avoided as much as possible in the 2 + n +2 Structure of the design through all layers of the hole. Such through holes in most cases can be connected to each other using a series of micro-hole drilling machinery or lining alternative, if we use, the ring must be big holes, tied for emissions to avoid the impact of the subsequent production of components of the plot, Makes it not be able to demonstrate their own advantage.


     If the reasons do not want to use-plated through hole, lining hole can be used as a reliable alternative. It uses mechanical FR-4 lengths in the drilling, electroplating then filled with epoxy resin. The simplest approach is to vacuum in the RCC copper foil lining to the repression, with copper foil on the RCC hole filled with epoxy resin. This method is good, but it is not applicable at all times, the thick plate in terms of the PCB, RCC copper foil on the number of epoxy resin is not enough, in addition especially in the high reliability requirements of the PCB board, with RCC Copper Foil epoxy resin as a filler is not the best, should select those optimized for reliability of the materials. In both cases the best use of Cypriot hole, this process using special silk screen method of filling the hole, curing the surface will be removed and re-fill electroplating copper.

Non-Futong sandwich

     1 + n +1 structure is also used in some non-Futong materials, use of laminated or coated (when it is the form of liquid epoxy resin) production methods. These dielectric materials cheaper, there are many advantages, such as can easily create micro-hole and an electroplating, thereby reducing such as micro-hole diameter. It could be used in thin coating of copper and is conducive to producing ultra-fine-pitch circuit, in the near future, these benefits can be used for 2 + n +2 structure. It also can be used for mixed-board technology, at the second level and m-1 layer using laser technology RCC production, and in these circumstances, the use of liquid epoxy resin as the most outside the first layer and the dielectric layer m At the same time can use two layers of the merits and to optimize the whole system. If the use of micro-production technology RCC hole lining, the general-Cypriots do not need process, and can achieve very good total surface; In contrast, the use of liquid epoxy resin produced by the outer can do more graphic resolution And further narrow-diameter hole.