Material Requirements for Automotive HDI PCB

The vigorous development of the electronics industry has promoted the rapid development of many industries. In recent years, electronic products have been widely used in the automotive industry. The traditional automotive industry has put more effort into mechanics, power, hydraulics and transmission. However, the modern automotive industry relies more on electronic applications, which play an increasingly important and potential role in automobiles. Automatic electrification is all about processing, sensing, information transfer, and recording, which cannot be achieved without a printed circuit board (PCB). Due to the requirements of automobile modernization and digitization, as well as human requirements for automobile safety, comfort, simple operation and digitization, PCBs have been widely used in the automotive industry, High Density Interconnect (HDI) PCBs, which may have cross-layer blind vias or Double layer structure.

In order to achieve high reliability and safety of automotive HDI PCBs, HDI PCB manufacturers must follow strict policies and measures.

Automotive PCB Types

In automotive circuit boards, traditional single-layer PCB, double-layer PCB and multi-layer PCB can be used, and in recent years, the wide application of HDI PCB has become the first choice for automotive electronic products. There is indeed an essential difference between ordinary HDI PCBs and automotive HDI PCBs: the former emphasizes practicality and versatility, serving consumer electronics, while the latter focuses on reliability, safety, and high quality.

It is necessary to state that because automobiles cover a wide variety of vehicles such as cars, trucks or trucks requiring different requirements for different performance expectations and functions, the regulations and measures that will be discussed in this article are just some general rules and do not include those rules. special case.

Classification and application of automotive HDIPCB

HDI PCB can be divided into single-layer HDI PCB, double-layer build-up PCB and three-layer build-up PCB. Here, layer refers to the layer of the prepreg.

Automotive electronics are typically used in two types of applications:

a. Automotive electronic control equipment will not operate effectively until it is used in conjunction with the vehicle's mechanical systems (such as engine, chassis and vehicle digital controls), especially electronic fuel injection systems, anti-lock braking systems (ABS), anti-skid control (ASC), Traction Control, Electronically Controlled Suspension (ECS), Electronic Automatic Transmission (EAT) and Electronic Power Steering (EPS).

b. In-vehicle automotive devices that can be used independently in the automotive environment and have nothing to do with car performance include automotive information systems or vehicle computers, GPS systems, automotive video systems, in-vehicle communication systems, and Internet device functions, which are implemented by devices supported by HDI PCBs , these devices are responsible for signal transmission and a lot of control.

Requirements for Automotive HDIPCB Manufacturers

Due to the high reliability and safety of automotive HDI printed circuit boards, automotive HDI PCB manufacturers must meet high-level requirements:

a. Automotive HDI PCB manufacturers must adhere to integrated management systems and quality management systems that play a key role in judging or supporting the management level of PCB manufacturers. Some systems cannot be owned by the PCB manufacturer until they are authenticated by a third party. For example, automotive PCB manufacturers must be ISO9001 and ISO/IATF16949 certified.

b. HDIPCB manufacturers must have solid technology and high HDI manufacturing capabilities. Specifically, manufacturers specializing in the manufacture of automotive circuit boards must manufacture circuit boards with a line width/space of at least 75μm/75μm and a two-layer structure. It is accepted 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. No modifications shall be made in subsequent manufacture unless approved and confirmed by the customer.

c. Automotive HDIPCB manufacturers must follow the strictest rules when selecting PCB raw materials as they play a key role in determining the reliability and performance of the final PCB.

Material Requirements for Automotive HDIPCB

• Core board and prepreg. They are the most basic and critical elements for making automotive HDI PCBs. When it comes to raw materials for HDI PCBs, the core board and prepreg are the main considerations. Typically, both the HDI core board and the dielectric layers are relatively thin. Therefore, one layer of prepreg is sufficient for use on consumer HDI boards. However, automotive HDI PCBs must rely on the lamination of at least two layers of prepreg, as a single layer of prepreg may result in lower insulation resistance if cavities or insufficient adhesives occur. After that, the end result could be the failure of the entire board or product.

• Solder mask. As a protective layer directly covering the surface circuit board, the solder mask also plays the same important role as the core board and prepreg. In addition to protecting the external circuit, the solder mask also plays a vital role in the appearance, quality and reliability of the product. Therefore, solder mask layers on automotive circuit boards must meet the most stringent requirements. Solder mask must pass a number of tests related to reliability, including thermal storage test and peel strength test.

Reliability Testing of Automotive HDIPCB Materials

A qualified HDI PCB manufacturer will never take material selection for granted. Instead, they had to do some testing on the board's reliability. The main tests concerning the reliability of automotive HDI PCB materials include CAF (Conductive Anode Wire) testing, high and low temperature thermal shock testing, weather temperature cycling testing and thermal storage testing.

• CAF test. It is used to measure the insulation resistance between two conductors. This test covers many test values such as minimum insulation resistance between layers, minimum insulation resistance between vias, minimum insulation resistance between buried vias, minimum insulation resistance between blind vias, and minimum insulation between parallel circuits resistance.

• High and low temperature thermal shock testing. This test is designed to test the resistance change rate that must be less than a certain percentage. Specifically, the parameters mentioned in this test include the resistance change rate between vias, the resistance change rate between buried vias and the resistance change rate between blind vias.

•Climate temperature cycle test. The board under test needs to be preconditioned before reflow soldering. In the temperature range of -40°C±3°C to 140°C±2°C, the board must be kept at the minimum temperature and the maximum temperature for 15 minutes. As a result, good boards do not suffer from lamination, white spots or explosions.

• High temperature storage test. This test focuses on the reliability of the solder mask, especially its peel strength. This test is considered the most stringent in terms of solder mask judgment.

Based on the test requirements described above, potential risks may occur if the substrate or raw material cannot meet customer requirements. Therefore, whether or not the material is tested can be a key factor in determining a qualified HDI PCB manufacturer.

There are many strategies and measures that can be used to judge an automotive HDI PCB manufacturer, including material supplier certification, technical conditions in the process, and parameter determination and application of accessories, etc.