Rogers RO4350B PCB Board for Anti Collision of Cars

Automobile has developed from pure mechanical structure to the participation of electronic parts. As early as the 1970s, the average value of automotive electronic parts was about $100. In 2000, this value has reached $1500 and it has climbed to $1500. In 2013, the global automotive electronic market has exceeded $150 billion. By 2020, this figure is expected to exceed $240 billion.

In addition, it is estimated that by 2020, the market value of automotive electronic systems with a market value of US $191 billion will soar to US $314.4 billion, with an average compound growth rate of 7.3%. Top class cars may contain 150 electronic control units, most of which are sensors and processors in the cockpit. According to some reports, 65% of the actual value of electronic products lies in the power system, automobile body and chassis, and most of them are related to digital power supply. The electronic value of electric vehicles will exceed 70%.

Circuit boards must be used in cars equipped with electronic equipment. In 2014, the Global Automotive PCB accounted for us $4.6 billion, which is estimated to exceed US $7 billion by 2020.

The application of vehicle system is to improve vehicle performance, which is now shown in three aspects: A. improving the environment refers to the process of saving fuel and reducing emissions, that is, from gasoline, natural gas and biofuels to hybrid and pure electricity. Electric vehicles have become the main development trend. b. Safety improvement refers to the reduction of traffic accidents, ranging from airbag to radar monitoring, stereo camera, night infrared monitoring, automatic collision avoidance and automatic driving. It is estimated that the self driving vehicle will be commercialized in three years. c. Convenience and comfort, from audio, video and air conditioning dedicated to cars to computers, mobile communications, the Internet, navigation and electronic charging, all of which must be more convenient and user-friendly.

Basic requirements for Automotive PCB

Quality assurance requirements

Automobile PCB manufacturers shall comply with ISO9001. PCB manufacturers fully comply with ISO9001:2008 quality management system and are committed to complying with the most stringent standards in manufacturing and assembly.

Automotive products have their particularity. In 1994, Ford, general motors and Chrysler established a quality control system QS9000 in the automotive industry. In the early 21st century, with the compatibility of ISO9001 standard, a new quality control system in the automotive industry was published, that is, ISO / iatf16949.

ISO / iatf16949 is a set of technical regulations for the global automotive industry. Based on ISO9001 and the special requirements of the automotive industry, it focuses more on defect prevention, reducing quality fluctuation and waste in the auto parts supply chain. When implementing ISO / iatf16949, special attention must be paid to the following five main tools: PPAP (production part approval process), which stipulates that products should be approved by customers before mass production or after modification; APQP (advanced product quality plan) stipulates that the quality plan and previous quality analysis shall be carried out before production, and then FMEA (failure mode and impact analysis) analysis shall be carried out, and measures to prevent potential failures of products shall be put forward. MSA (measurement system analysis) must analyze the changes of measurement results to confirm the measurement reliability, SPC (statistical process control) Master production procedures and use statistical techniques to change product quality. Therefore, the first step for PCB manufacturers to enter the automotive electronics market is to obtain iatf16949 certificate.

Basic requirements for performance

a. High reliability

Automobile reliability mainly comes from two aspects: service life and environmental resistance. The former refers to the fact that normal operation can be guaranteed within the service life, while the latter refers to the fact that PCB functions remain unchanged when the environment changes.

In the 1990s, the average life of the automobile was 8-10 years, and now it is 10-12 years, which means that the automotive electronic system and PCB should be within this range.

In the process of application, the vehicle should withstand the impact of climate change, from extremely cold winter to hot summer, from sunshine to rain, and environmental changes caused by the temperature rise caused by its own driving. In other words, automotive electronic systems and PCBs must withstand a variety of environmental challenges, including temperature, humidity, rain, acid mist, vibration, electromagnetic interference and current surge. In addition, because PCB is assembled inside the car, it is mainly affected by temperature and humidity.

b. Light weight and small volume

Lightweight, miniature cars are conducive to energy conservation. Lightweight comes from reducing the weight of each component. For example, some metal parts are replaced by engineering plastic parts. In addition, automotive electronic equipment and PCB should be miniaturized. For example, the volume of ECU (electronic control unit) in automotive applications is about 1200 cm3, which began in 2000, and less than 300 cm3, which decreased four times. In addition, the starting point firearms have changed from mechanical firearms connected through wires to electronic firearms connected through flexible wires with PCB inside, and the volume and weight have been reduced by more than 10 times.

The lightweight and miniaturization of PCB comes from the increase of density, the reduction of area, the reduction of thickness and multilayer.

Performance attributes of automobile PCB

Various automotive PCBs

Cars combine mechanical and electronic equipment. Modern automotive technology combines traditional technology and advanced science and technology, such as manual interior decoration components and advanced GPS. In modern automobile, there are electronic devices with different functions in different positions and different types of PCB derive different functions.

According to the substrate materials, Automotive PCB can be divided into two categories: Inorganic Ceramic Based PCB and organic resin based PCB. Ceramic Based PCB has high temperature resistance and excellent dimensional stability, so that it can be directly applied to high temperature motor system. However, it has the characteristics of poor ceramic manufacturability and high cost. At present, with the development of resin substrate materials in heat resistance, resin based PCB has been widely used in automobiles with different properties and substrate materials at different positions.

Generally speaking, flexible PCB and rigid PCB are used in common instruments to indicate vehicle speed and mileage and air conditioning equipment. Double layer or multi-layer PCB and Flex PCB are used for audio and video entertainment equipment in cars. For communication and wireless positioning equipment and safety control equipment, multi-layer PCB, HDI printed circuit board and Flex PCB are applied. For automobile motor control system and power transmission control system, special boards, such as metal substrate and rigid flexible PCB, shall be used. For micro automobile, component embedded PCB shall be used. For example, microprocessor chip shall be used in power controller, Directly embedded in the power controller PCB. As another example, the PCB of the embedded element is also used in the navigation device and stereo imaging device of the automatic support system.

Different reliability requirements of PCBs in different positions

In terms of public safety, automobile belongs to the category of high reliability products. Therefore, automobile PCB must pass some reliability tests, except for general requirements such as size, size, mechanical and electrical performance.

a. Thermal cycle test (TCT)

According to the five grades classified according to different positions of the vehicle, the PCB thermal cycle temperature is summarized in Table 1 below.

PCB thermal cycle temperature

b. Thermal shock test

Automotive PCBs are increasingly used in high temperature environments, especially for thick copper PCBs that must deal with external heat and self heating. As a result, Automotive PCB has higher requirements for heat resistance.

c. Temperature and humidity deviation (THB) test

Because the Automotive PCB is in a variety of environments, including rainy days or humid environments, it is necessary to conduct THB test on it. The test conditions include the following elements: temperature (85  degree Celsius), humidity (85% RH) and bias (DC 24V, 50V, 250V or 500V).

The caf migration of PCB must be considered in THB test. Caf usually occurs between adjacent vias, vias and lines, adjacent lines or adjacent layers, resulting in reduced insulation or even short circuit. The corresponding insulation resistance depends on the distance between through holes, wires and layers.

Manufacturing characteristics of automobile PCB

High frequency substrate

Automobile anti-collision / predictive braking safety system plays the role of military radar equipment. Because the automobile PCB is responsible for transmitting microwave high-frequency signals, it is necessary to use the substrate with low dielectric loss together with the ordinary substrate material PTFE. Different from FR4 materials, PTFE or similar high-frequency matrix materials require special drilling speed and feed speed in the drilling process.

Thick copper PCB

Due to high density, high power and hybrid power, automotive electronic products bring more heat energy, while electric vehicles often need more advanced power transmission system and more electronic functions, which puts forward higher requirements for heat dissipation and high current.

It is relatively easy to make thick copper double-layer PCB, while it is much more difficult to make thick copper multi-layer PCB. The key lies in thick copper image etching and thickness vacancy filling.

The internal paths of thick copper multilayer PCBs are all thick copper, so the pattern transfer photo dry film is also relatively thick, which requires high etching resistance. The pattern etching time of thick copper will be very long, and the etching equipment and technical conditions are in the best state to ensure the complete wiring of thick copper. When the external thick copper wiring is manufactured, it can be combined between the laminated relatively thick copper foil and the graphical thick copper layer, and then the film gap etching can be carried out. The anti plating dry film of pattern plating is also relatively thick.

The surface difference between the internal conductor of thick copper multilayer PCB and the insulating substrate material is large. The ordinary multilayer board lamination can not completely fill the resin and produce a cavity. In order to solve this problem, thin prepreg with high resin content should be used as much as possible. The copper thickness of internal wiring on some multilayer PCBs is uneven, and different prepregs can be used in areas with large or small copper thickness differences.

Component embedding

In order to increase the assembly density and reduce the component size, the PCB of embedded components is widely used in mobile phones, which is also required by other electronic devices. Therefore, component embedded PCB is also used in automotive electronic equipment.

According to different component embedding methods, there are many manufacturing methods for component embedded PCB. There are four main manufacturing methods for component embedded PCB used in automotive electronic products, as shown in Figure 1 below.

There are four main manufacturing methods for component embedded PCB

Among these manufacturing types, the excavation type (type A in Figure 1) follows the following process: excavation, and then SMD assembly by reflux or conductive adhesive. The lamination type (type B in Fig. 1) is realized by reflow through thin SMD components on the internal circuit, or refers to thin component manufacturing. The ceramic type (type C in Figure 1) refers to a thick film assembly printed on a ceramic substrate. The module type (type D in Figure 1) follows the following steps: SMD assembly by reflow and resin packaging. The modular component embedded PCB has relatively high reliability and is more suitable for the requirements of automobile for heat resistance, moisture resistance and vibration resistance.

HDI Technology

One of the key functions of automotive electronics is entertainment and communication, in which smart phones and tablets need HDI PCB. Therefore, the technologies contained in HDI PCB (such as microporous drilling and electroplating and lamination positioning) are applied in Automotive PCB manufacturing.

So far, with the rapid change of automotive technology and the continuous upgrading of automotive electronic functions, the application of PCB will increase exponentially. Engineers and PCB manufacturers must focus on new technologies and new content so that they can meet higher automotive requirements.