Rushing development of electronic industry drives numerous industries to rapid progress. Recent years have witnessed increasingly wide applications of electronic products in automotive industry. Traditional automotive industry strived more for mechanics, power, hydraumatic and transmission. Modern automotive industry, however, depend more on electronic applications that are playing an increasingly significant and potential role in automotives. Automatic electrization is all used on handling, sensing, information transmission and recording that can never be achieved without printed circuit boards (PCBs). Due to demands of automotive modernization and digitalization, along with human's demands towards security, comfort, simple operation and digitalization of automotives, PCBs have been widely applied in automotive industry, ranging from ordinary single-layer PCBs, double-layer PCBs to complicated multi-layer PCBs or to high density interconnect (HDI) PCBs that possibly carry cross-layer blind vias or double build up layers.
To achieve high reliability and security of automotive HDI PCBs, stringent strategies and measures have to be conformed to by HDI PCB manufacturer, which is the leading point this article will focus on.
Automotive PCB Type
Among automotive circuit boards, traditional single-layer PCBs, double-layer PCBs and multi-layer PCBs are available while recent years have seen wide applications of HDI PCBs that have become the first selection for automotive electronic products. An essential difference does occur between ordinary HDI PCBs and automotive HDI PCBs: the former emphasizes practicability and multiple functions, serving consumer electronics while the latter strives for reliability, security and high quality.
It's necessary to illustrate that because automotives cover a wide classification of vehicles such as cars, trucks or lorries calling for different requirement for different performance expectations and functions, regulations and measures that will be discussed in this article are just some rules for universal applications excluding those special cases.
Automotive HDI PCB Classification and Applications
HDI PCBs can be classified into single-layer HDI PCB, double-layer build up PCB and three-layer build-up PCB. Here, layer refers to the layer of prepreg.
Automotive electronic products are usually applied in two categories:
a. Automotive electronic control devices that won't effectively functions until they cooperate with mechanical systems on vehicles such as engine, chassis and vehicle digital control, specifically electronic fuel injection system, anti-lock brake system (ABS), anti-slip control (ASC), traction control, electronic control suspension (ECS), electronic automatic transmission (EAT) and electronic power steering (EPS).
b. On-board automotive devices that can be independently used in automotive environment and have nothing to do with automotive performance including automotive information system or vehicle computer, GPS system, automotive video system, on-board communication system and Internet equipment functions of which are implemented by devices supported by HDI PCBs that are responsible for signal transmission and numerous control.
Requirement on Automotive HDI PCB Manufacturers
Due to high reliability and security of automotive HDI PCBs, automotive HDI PCB manufacturers have to conform to high-level requirement:
a. Automotive HDI PCB manufacturers must stick to an integrated administration system and quality management system that play a key role in judging or supporting management level of PCB manufacturers. Some systems fail to be owned by PCB manufacturers until being identified by third-party authentication. For example, automotive PCB manufacturers have to be certified by ISO9001 and ISO/TS16949.
b. HDI PCB Manufacturers have to be equipped with solid technologies and high HDI fabrication capability. Specifically speaking, manufacturers specializing in automotive circuit board fabrication have to manufacture boards with line width/spacing to be at least 75μm/75μm and two-layer build up. It is accepted that HDI PCB manufacturer has to feature capability index of process (CPK) at least 1.33 and equipment manufacturing capacity (CMK) at least 1.67. No modification is allowed to be made in later manufacturing unless customers' approval and confirmation are achieved.
c. Automotive HDI PCB manufacturers have to follow the most stringent rules in selecting PCB raw materials as they play a key role in determining reliability and performance of final PCBs.
Material Requirement on Automotive HDI PCBs
• Core board and Prepreg. They are the most fundamental and critical element in fabricating automotive HDI PCBs. When it comes to raw material of HDI PCBs, core board and prepreg are leading considerations. Generally, both HDI core board and dielectric layer are relatively thin. Therefore, one layer of prepreg is sufficient to be used in consumer HDI boards. Automotive HDI PCBs, however, have to depend on lamination of at least two layers of prepreg because a single layer of prepreg possibly leads to insulating resistance reduction if cavity or insufficient adhesive occurs. Afterwards, the final result may be failure of the whole board or product.
• Solder Mask. As a protective layer directly covering on the surface circuit boards, solder mask also plays an important role of the same significance as core board and prepreg. Apart from protecting external circuits, solder mask also plays an essential part in appearance, quality and reliability of products. As a result, solder mask on circuit boards for automotives has to conform to the strictest requirement. Solder mask has to pass multiple tests concerning reliability including thermal storage test and peel-off strength test.
Tests Concerning Reliability of Automotive HDI PCB Material
Qualified HDI PCB manufacturers never take material selections for granted. Instead, they have to implement some tests on reliability of circuit boards. The main tests concerning reliability of automotive HDI PCB materials include CAF (Conductive Anodic Filament) test, high and low temperature thermal shock test, weather temperature cycling test and thermal storage test.
• CAF Test. It is implemented to measure insulation resistance between two conductors. This test covers lots of test values such as minimum insulation resistance between layers, minimum insulation resistance between thru holes, 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 Test. This test aims to test resistance change rate that has to be less than a certain percent. Specifically, parameters mentioned in this test include resistance change rate between thru holes, resistance change rate between buried vias and resistance change rate between blind vias.
• Weather Temperature Cycling Test. Boards to be tested need to go through pre-processing prior to reflow soldering. Within the temperature range from -40°C±3°C to 140°C±2°C, boards have to maintain in the lowest temperature and highest temperature for 15 minutes. As a result, lamination, white spot or explosion won't occur to qualified circuit boards.
• Thermal Storage Test. This test mainly works on reliability of solder mask, especially its peel-off strength. This test can be regarded as the most stringent in terms of solder mask judgment.
Based on the requirement of tests introduced above, some potential risk will take place if substrate material or raw material fails to meet demands of customers. Therefore, whether to carry out tests on materials can be a crucial element determining a qualified HDI PCB manufacturer.
Lots of strategies and measures to judge an automotive HDI PCB manufacturer are available, ranging from material supplier authentication, in-process technical conditions and parameter determination and application of accessories etc. In search for a reliable HDI PCB manufacturer, they can be important ingredients in determining and judging its reliability as reference.
PCBCart has been manufacturing HDI PCBs for numerous companies for over a decade. We are capable of making HDI circuit boards up to 24 layers in various structures. Our circuit boards are widely used in advanced applications including mobile phones, touch-screen devices, laptop computers, digital cameras, medical devices, etc. You may check the following articles to learn more about HDI PCBs and our HDI PCB production services.
• Something You Must Know about HDI
• 3 Keys to Designing a Successful HDI PCB
• Applications and Types of PCBs for Automotive Industry
• Custom HDI PCB Fabrication Service Starts from 1 piece
• PCB Design Tips to Better Take Advantage of PCBCart's Capabilities And Save Cost