The rapid development of electronic industry promotes the rapid development of many industries. In recent years, electronic products are more and more widely used in automobile industry. The traditional automotive industry has made more efforts in mechanics, power, hydraulics and transmission. However, the modern automotive industry relies more on electronic applications which play an increasingly important and potential role in the automotive industry. Automatic electrification is all used for processing, sensing, information transmission and recording, which PCB can never achieve. Due to the needs of automobile modernization and digitization, as well as people's requirements for automobile safety, comfort, simple operation and digitization, PCB has been widely used in automobile industry, from ordinary single-layer PCB, double-layer PCB to complex multilayer PCB.
To achieve high reliability and safety of automobile HDI PCB, strict strategies and measures must comply with the requirements of HDI PCB manufacturer.
Auto PCB type
In automotive circuit boards, traditional single-layer PCB, double-layer PCB and multi-layer PCB are available. In recent years, the wide application of HDI PCB has become the first choice of automotive electronic products. There are essential differences between ordinary HDI PCB and automotive HDI PCB: the former emphasizes practicability and multi-function, providing services for consumer electronic products, while the latter strives for reliability, safety and high quality.
It is necessary to point out that because automobiles cover a wide range of vehicle categories such as autos, trucks, there are different requirements for different performance expectations and functions. The rules and measures discussed in this paper are only some rules for general application in addition to these special cases.
Classification and application of auto HDI PCB
HDI PCB can be divided into single-layer HDI PCB, double-layer build-up PCB and three-layer build-up PCB. Here, the layer refers to the prepreg layer.
Automotive electronic products are generally divided into two categories:
a: Automotive electronic control devices cannot operate effectively until they work with mechanical systems on the vehicle, such as engine, chassis and vehicle digital control, especially electronic fuel injection system, anti lock braking system (ABS), anti skid control (ASC), traction control, electronic suspension (ECS), electronic automatic transmission (eat) and electronic power steering (EPS).
b: The on-board vehicle equipment that can be used independently in the automotive environment and has nothing to do with vehicle performance includes vehicle information system or on-board computer, GPS system, vehicle video system, vehicle communication system and Internet equipment. The functions are realized by the equipment supported by HDI PCB, which is responsible for signal transmission and multiple control.
Requirements for auto HDI PCB manufacturers
Due to the high reliability and safety of auto HDI PCB, the manufacturer of auto HDI PCB must meet the high level requirements
a: Auto HDI PCB manufacturers must adhere to the integrated management system and quality management system which play a key role in judging or supporting the management level of PCB manufacturers. Some systems cannot be owned by PCB manufacturers until they are identified by third party certification. For example, auto PCB manufacturers must pass ISO9001 and ISO / TS16949 certification.
b: HDI PCB manufacturers must be equipped with strong technology and high HDI manufacturing capacity. Specifically, a manufacturer specializing in the manufacture of automotive circuit boards must produce boards with a line width / spacing of at least 75 μ M / 75 μ m and double stacked. It is generally believed that HDI PCB manufacturers must have at least 1.33 process capability index (CPK) and at least 1.67 equipment manufacturing capacity (CMK). Modifications in future manufacturing are not allowed unless approved and confirmed by the customer.
c: Automotive HDI PCB manufacturers must follow the most stringent rules for selecting PCB raw materials because they play a key role in determining the reliability and performance of the final PCB.
Material requirements for automotive HDI PCB
· Core substrate and prepreg. They are the most basic and key factors in manufacturing automobile HDI PCB. When it comes to the raw materials of HDI PCB, the core substrate and prepreg are the main considerations. Generally, HDI core substrate and dielectric layer are relatively thin. Therefore, one layer of prepreg is sufficient for consumer HDI boards. However, automotive HDI PCB must rely on lamination of at least two layers of prepreg, because a single layer of prepreg may result in reduced insulation resistance in the event of cavities or insufficient adhesive. After that, the final result may be a failure of the entire circuit board or product.
· Solder mask. As the protective layer directly covering the surface circuit board, the welding mask also plays an important role as the core board and prepreg. In addition to protecting external circuits, solder mask plays an important role in the appearance, quality and reliability of products. As a result, the solder mask used on the circuit board of the automobile must meet the most stringent requirements. Solder mask must pass a number of reliability tests, including thermal storage test and peel strength test.
Reliability test of auto HDI PCB material
Qualified HDI PCB manufacturers never take material selection for granted. Instead, they have to test the reliability of the board. The main tests of automotive HDI PCB material reliability include CAF test, high temperature and low temperature thermal shock test, weather temperature cycle test and thermal storage test.
· CAF test. It is used to measure the insulation resistance between two conductors. The test covers many test values, such as minimum insulation resistance between layers, minimum insulation resistance between through holes, minimum insulation resistance between buried holes, minimum insulation resistance between blind holes and minimum insulation resistance between parallel circuits.
· high and low temperature thermal shock tests. The purpose of this test is to test the rate of change of resistance that must be less than a certain percentage. Specifically, the parameters mentioned in this test include the resistance change rate between through holes, the resistance change rate between buried holes and the resistance change rate between blind holes.
· weather temperature cycle test. The PCB to be tested needs to be pretreated before reflow soldering. In the temperature range of – 40 ° C ± 3 ° C to 140 ° C ± 2 ° C, the circuit board must be kept at the minimum and maximum temperature for 15 minutes. As a result, no lamination, white spots or explosions will occur on qualified boards.
· heat storage test. This test is mainly used for the reliability of solder mask, especially its peel strength. This test can be regarded as the most stringent in terms of solder mask judgment.
According to the requirements of the above test, if the substrate materials or raw materials can not meet, there will be some potential risk customer needs. Therefore, whether the material is tested may be a key factor in determining a qualified HDI PCB manufacturer
Many strategies and measures can be used to judge the manufacturer of auto HDI PCB, including material supplier certification, determination of technical conditions and parameters in the process, and application of accessories. Looking for reliable HDI PCB manufacturers can be an important factor in determining and judging their reliability.