Embedded PCB Technology
Nowdays the assembly density of components on PCB is getting higher and higher follow the miniaturization, thinning and high speed of electronic products. And the transmission speed of the electric signal is getting faster and faster, it is difficult to meet the higher assembly requirements only increasing the wiring density and multilayer of PCB. In order to improve the integrity of transmission signals, high frequency and high-speed digital signals in high-speed computing systems and communication devices are transmitted, It is usually achieved by strictly controlling the characteristic impedance (Z0) in the transmission line and using a large number of matched resistors or capacitors. However, such a large number of chip resistors and capacitors will occupy a large part of the PCB area and space, affecting the limit of PCB to achieve high density assembly. At the same time, these conductive holes and conductors used to match resistors (or capacitors) have inductive capacitance. It will affect the decoupling effect of signal transmission impedance and capacitance, thus generating the integrity of transmission line signals.
If these elements are embedded in the printed circuit board, the space for installing SMD on the same area will be greatly increased. At the same time, it can also improve the impedance matching requirements of signal transmission characteristics. In recent years, printed circuit boards with embedded components such as resistors and capacitors have developed rapidly. Although some technologies are not perfect at present, the superiority of it is more and more valued by the electronics manufacturing industry. As one of the development directions of printed circuit boards, it will become increasingly mature and widely used.
Types of printed versions embedded in passive components
Embedded passive PCB can be classified into four types according to their type and mode.
- Embedded Resistor PCE :The passive element embedded in the printed board is the resistance.
- Embedded Capacitor PCI: The passive element embedded in the printed board is the capacitance.
- Embedded Inductor PCB: The passive element embedded in the printed board is the inductor.
- Embedded Passive PCB: printed boards embedded in various passive components.
When PCB is embedded with two or three kinds of components, such as resistors, capacitors and inductors, it can be called passive PCB.
Application range, advantages and disadvantages of embedded passive printed boards
Application range
Embedded passive PCB is widely used at home and abroad, and is mainly used in computers (such as giant computer mainframe, information processor). PC card, IC card and all kinds of terminal equipment, communication system (such as cellular launch platform ATM system, portable communication equipment, etc.), test instrument and test equipment (such as IC scan card, interface card, load board tester), Aerospace electronic products (such as space aircraft, electronic devices on artificial satellites, etc.), consumer based electronic devices (such as potentiometers, heaters), medical electronic devices (such as scanners, ttms), and electronic control systems in military equipment (such as cruise missiles, radar unmanned reconnaissance machines, shields, etc.)
Advantages and disadvantages
Embedding a large number of embeddable passive elements into printed circuit boards (including HDI boards), making PCB components more lightweight and lightweight. Embedded printed boards with passive components have the following advantages:
Improving the degree of high density of PCB:
Because the discrete (non buried) passive components are not only assembled in large quantities, but also occupy a large amount of space on the printed board surface, such as the GSM phone contains more than 500 passive components, accounting for about 50% of the area of the printed board panel, such as embedding 50% of the passive components into the printed board (or HDI board). The size of the printed board surface can be reduced by about 25%, thus greatly reducing the number of through holes and reducing and shortening the connecting wires. It can not only increase the flexibility and degree of freedom of PCB design and wiring, but also reduce the amount of wiring and shorten the length of wiring, thus greatly increasing the degree of high density of printed board (or HDI board) and shortening the transmission path of the signal.
Improving the reliability of PCB assembly
Embedding the passive components into PCB can significantly improve the reliability of PCB (or HDUBUM) assembly. Because of this process, the welding (SMTAK PHT) point of the printed board surface is greatly reduced, thus the reliability of the board is improved and the probability of the failure caused by the welding point is greatly reduced.
In addition, buried passive components can be effectively protected and improved reliability. Because these passive components are embedded inside the PCB instead of discrete (or discrete) passive components, they are soldered (or bonded) by pins.
The connection pad on PCB surface will not be eroded or damaged by moisture or harmful gas in the atmosphere. Therefore, embedding passive components can significantly improve the reliability of PCB assemblies.
Improving the electrical properties of PCB assembly
Embedding passive components into high-density PCB makes the electrical performance of electronic interconnect improved significantly. Because it eliminates the need to connect the pads, wires and the wires formed after soldering. Any such loop will inevitably produce parasitic effects, namely stray capacitance and parasitic inductance. And this parasitic effect will also become more serious with the increase of the signal frequency or the forward time of the pulse square wave. Eliminating this type of fault will undoubtedly improve the electrical performance of PCB assemblies (signal transmission distortion is greatly reduced). At the same time, because the passive components are embedded inside the printed board, the surrounding is closely protected. It will not change its function value (resistance value, capacitance value and inductance value) because of the dynamic changes in the working environment, and make it in a very stable state, which is beneficial to improving the stability of the function of passive components and reducing the function of passive components. The probability of failure.
Saving the cost of product manufacturing
The cost of products or PCB assemblies can be obviously reduced by adopting this process. In the study of the radio frequency circuit (EP RF) model embedded in passive components, the printed board substrate (embedded in the same passive component) is equivalent to the low temperature co fired ceramic substrate (LTCC). According to the cost of the statistical component, the cost can be saved by 10%, the cost of the substrate can be saved by 30%, and the cost of assembly (welding) can be saved by 40% . At the same time, because the assembly process and the sintering process of the ceramic substrate are difficult to control, the printed board substrate embedded in the passive component (EP) can be completed by the traditional PCB manufacturing process, thus greatly improving the production efficiency.
Of course, any process has its limitations. The shortcomings of embedded PCB are:
One is that the passive components that are buried at present are small in function value. For the components of large resistance value, capacitance value and inductance value, it is necessary to develop passive component materials with large functional characteristics.
Secondly, it is difficult to control the error control of the function characteristic value of the embedded passive components, especially the plane type embedded passive component material with screen printing, which is more difficult to control the error of the function characteristic value error. Although laser technology can be used to repair and control the characteristic and functional error of embedded passive components, not all embedded passive components can be repaired by this method, so as to achieve the design requirements. The latest research of film resistance embedding method has greatly improved the accuracy of resistance value.