Automotive HDI PCB Classification and Application

The rapid development of the electronics industry has promoted the rapid development of many industries. In recent years, electronic products have become more and more widely used in the automotive industry. The traditional auto industry has more efforts in mechanics, power, hydraulics and transmission. However, the modern automotive industry relies more on electronic applications that play an increasingly important and potential role in automobiles. Automatic electrification is all about processing, sensing, information transfer and recording, something that a printed circuit board (PCB) could 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, PCBs have been widely used in the automotive industry, from ordinary single-layer PCBs, double-layer PCBs to complex multi-layer PCBs. Layer PCB or High Density Interconnect (HDI) PCB, possibly with cross-layer blind vias or dual build layers.

To achieve high reliability and safety of automotive HDI PCBs, strict policies and measures must be followed by HDI PCB manufacturers, which will be the focus of this article.

Automotive PCB Types

In automotive circuit boards, traditional single-layer PCB, double-layer PCB and multi-layer PCB are available, while the wide application of HDI PCB in recent years 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 multi-functionality, serving consumer electronics, while the latter strives for reliability, safety, and high quality.

It is necessary to state that because automobiles cover a broad classification of vehicles such as cars, trucks or trucks requiring different requirements for different performance expectations and functions, the rules and measures that will be discussed in this article are just some of the general applications beyond these special cases. rule.

Automotive HDI PCB Classification and Application

HDI PCBs can be divided into single-layer HDI PCBs, double-layer build-up PCBs and triple-layer build-up PCBs. Here, the layer refers to the prepreg layer.

Automotive electronics are generally divided into two categories:

a. Automotive electronic controls cannot operate effectively until they cooperate with the mechanical systems on the vehicle (such as the 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 automotive performance include automotive information systems or in-vehicle computers, GPS systems, automotive video systems, in-vehicle communication systems, and Internet devices. The functions are implemented by devices supported by HDI PCB, responsible for signal transmission and multiple kind of control.

Requirements for Automotive HDI PCB Manufacturers

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

a. Automotive HDI PCB manufacturers must adhere to comprehensive management systems and quality management systems that play a key role in judging or supporting the management level of PCB manufacturers. Certain systems cannot be owned by a PCB manufacturer until identified by a third-party certification. For example, automotive PCB manufacturers must be ISO9001 and ISO/TS16949 certified.

b. HDI PCB manufacturers must be equipped with solid technology and high HDI manufacturing capabilities. Specifically, manufacturers specializing in automotive circuit board fabrication must make boards with a line/space of at least 75μm/75μm and double-stacked. It is generally 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. Modifications in future manufacturing are not permitted unless approved and confirmed by the customer.

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

Material Requirements for Automotive HDI PCB

• Core board and prepreg. They are the most basic and critical factors for making automotive HDI PCBs. The core board and prepreg are the main considerations when it comes to raw materials for HDI PCBs. Typically, both the HDI core board and the dielectric layers are relatively thin. Therefore, one layer of prepreg is sufficient for 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 can lead to lower insulation resistance in the event of cavities or insufficient adhesive. After that, the end result could be the failure of the entire board or product.

• Welding mask. Solder mask also plays an equally important role as core board and prepreg as a protective layer directly over surface circuit boards. Besides protecting external circuits, solder mask also plays a vital role in product appearance, quality and reliability. As a result, solder masks on circuit boards for automobiles must meet the most stringent requirements. Solder masks must pass several tests for reliability, including thermal storage tests and peel strength tests.

Reliability testing of automotive HDI PCB materials

Qualified HDI PCB manufacturers never take material selection for granted. Instead, they had to do some testing on the board's reliability. The main tests on the reliability of automotive HDI PCB materials include CAF (Conductive Anode Wire) test, high 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. 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 resistance between parallel circuits .

• High and low temperature thermal shock tests. 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.

• Weather temperature cycle test. The board to be tested needs to be preconditioned before reflow soldering. The board must be kept at the minimum and maximum temperature for 15 minutes within the temperature range of -40°C ± 3°C to 140°C ± 2°C. As a result, no lamination, white spots, or explosions will occur on qualified boards.

• Thermal storage test. This test is mainly used for the reliability of solder mask, especially its peel strength. In terms of solder mask judgment, this test can be considered the most stringent.

According to the requirements of the above test, if the substrate material or raw material cannot meet the needs of customers, some potential risks will occur. Therefore, whether or not a 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, in-process specification and parameter determination, and application of accessories, etc. Find a reliable HDI PCB manufacturer who can be an important factor in determining and judging their reliability.