The rapid development of electronic industry promotes the rapid development of PCB industry. In recent years, electronic products are more and more widely used in the automotive industry. The traditional automobile industry has made more efforts in mechanics, power, hydraulic and transmission. However, the modern automobile industry relies more and more on the electronic application which plays an increasingly important role in the automobile.
Automatic electrification is all used for processing, sensing, information transmission and recording, which PCB can never achieve. Due to the needs of modernization and digitalization of automobile, as well as people's requirements for automobile safety, comfort, simple operation and digitalization, PCB has been widely used in automobile industry, from ordinary single-layer PCB, double-layer PCB to complex multi-layer PCB or high-density interconnection automobile HDI PCB.
To achieve high reliability and safety of automobile HDI PCB, strict strategies and measures must comply with the requirements of custom HDI PCB manufacturing, which is the focus of this paper.
In the automobile circuit board, the traditional single-layer PCB, double-layer PCB and multi-layer PCB are available. In recent years, the extensive application of HDI PCB has become the first choice of automobile electronic products.
There are essential differences between ordinary HDI PCB and automobile HDI PCB: the former emphasizes practicability and multi-function to provide services for consumer electronic pcb products, while the latter strives for reliability, safety and high quality.
It is necessary to explain that because automobiles cover a wide range of vehicle categories, such as automobiles, trucks, which require 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.
HDI PCB can be divided into single-layer HDI PCB, double-layer construction PCB and three-layer Multilayer PCB, or even any layer interconnection (Any layer HDI).
Automotive electronic products are usually divided into two categories
a. Automobile electronic control devices must not be able to operate effectively before cooperating with the mechanical systems (such as engine, chassis and vehicle digital control) on the vehicle, especially electronic fuel injection system, anti lock braking system (ABS), antiskid control (ASC), traction control, electronic control suspension (ECS), electronic automatic transmission (EAT) and electronic power steering (EPS).
b. The on-board vehicle equipment which can be independently used in the vehicle environment and has nothing to do with the vehicle performance, including the vehicle information system or on-board computer, GPS system, vehicle video system, on-board communication system and Internet equipment functions are realized by the equipment supported by HDI PCB, responsible for signal transmission and multiple controls.
Due to the high reliability and safety of automobile HDI PCB, automobile HDI PCB manufacturer must meet the high level requirements:
a. Automobile HDI PCB manufacturers must adhere to the integrated management system and quality management system that play a key role in supporting PCB manufacturers management level. Some systems cannot be owned by PCB manufacturers until they are certified and identified by a third party. For example, automobile PCB manufacturers must pass ISO9001 and ISO / TS16949 certification.
b. HDI PCB manufacturers must be equipped with robust technology and high HDI manufacturing capabilities. Specifically, PCB manufacturers specializing in the manufacture of automotive circuit boards must manufacture boards with a line width / spacing of at least 75 μm / 75 μm and double-layer stacking(2+n+2). It is generally believed that HDI PCB manufacturers must have a process capability index (CPK) of at least 1. 33 and a device manufacturing capability (CMK) of at least 1. 67. Unless approved and confirmed by the customer, modification is not allowed in the future manufacturing.
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.
Core plate and prepreg
They are the most basic and key factors in manufacturing automobile HDI PCB. When it comes to raw materials of HDI PCB, core board and prepreg are the main factors to be considered. In general, the HDI core board and dielectric layer are relatively thin. One layer of prepreg is enough for consumer electronics HDI board. However, the automotive HDI PCB must rely on the lamination of at least two layers of prepreg, because if there is a cavity or insufficient adhesive, the single layer of prepreg may cause the insulation resistance to decrease. After that, the final result may be a failure of the entire circuit board or product.
As a protective layer directly covering the surface circuit board, the solder 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 soldermask used in automobile circuit board must meet the most stringent requirements. The soldermask must pass a number of reliability tests, including thermal storage test and peel strength test.
Qualified HDI PCB manufacturers never take material selection for granted. Instead, they have to test the reliability of the boards. The main tests on the reliability of automobile high quality HDI PCB materials include CAF (conductive anode wire) test, high and low temperature thermal shock test, weather temperature cycle test and thermal storage test.
1. CAF test
It is used to measure the insulation resistance between two conductors. This test covers many test values, such as the minimum insulation resistance between layers, the minimum insulation resistance between through holes, the minimum insulation resistance between buried holes, the minimum insulation resistance between blind holes and the minimum insulation resistance between parallel circuits.
2. High and low temperature thermal shock test
The purpose of this test is to test a resistance change rate 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.
3. Weather temperature cycle test
The plates to be tested need 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. Therefore, the qualified circuit board will not have delamination, white spot or explosion.
4. 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 the judgement of soldermask.
According to the above test requirements, if the substrate material or raw material cannot meet the requirements, there will be some potential risks. Therefore, testing of materials may be a key factor in determining a qualified HDI PCB Factory.
Many strategies and measures can be used to judge the manufacturer of automobile HDI PCB, including material supplier certification, determination of technical conditions and parameters in the process, application of accessories, etc.
They can be an important factor to determine and judge your automotive HDI board’s reliability when you are looking for reliable manufacturers of HDI PCB.