What factors can cause PCB failure in the production of automotive PCBs, the common environmental loads and PCB assembly and their possible failure modes are as follows:

Possible failure modes

• Plated through-holes or internal copper cracks
• Cracks in the outer copper layer
• Microvia Cracks
• Semi-cured cracks
• Solder mask crack

Electrochemical Migration on PCB Surface

• PCB environmental load
• Temperature cycling and storage
• bending
• shock
• humidity
• Combination of several loads

• Lamination technology

The above factors will affect the reliability of automotive PCB manufacturing. In order to manufacture high-quality automotive PCBs, let us understand the performance requirements of automotive PCBs and how to test them to ensure high quality.

Compact size and light

Reasonably reducing the size and weight of the automotive can save more fuel, electricity, energy, and improve environmental protection. Therefore, the size of the automotive is becoming more and more compact. Due to the automotive’s overall size reduction, the automotive PCB will inevitably become more compact and lighter.

High reliability

The high reliability of automotive PCB means that within the normal service life of the automotive, the PCB can maintain good stable performance in the face of different complex environments. In other words, automotive PCBs must be able to withstand a variety of environmental interfaces, including humidity resistance, water resistance, heat resistance, corrosion resistance, vibration resistance, and electromagnetic interference resistance.

Automotive PCB reliability is closely related to our safety, so various reliability tests must be passed when manufacturing automotive PCBs. Automotive PCBs in different locations require different reliability tests. Common tests include:

1) Thermal shock test

Automotive PCBs must normally work in a high-temperature environment caused by external heat or the high temperature from self-generated heat. Automotive PCBs must withstand the shock of sudden changes in heat, and we need to conduct thermal shock tests on automotive PCBs.

2) Thermal cycle test

According to different positions of the automotive, the PCB thermal cycle test has different levels. The commonly used PCB thermal cycle temperatures are as follows:

3) Temperature and humidity deviation test

Changes in temperature and humidity are one of the essential factors that cause the failure of automotive PCBs, although automotive manufacturers have taken various measures to solve this problem; such as:

• Optimized materials
• Self-heating

But self-heating is often only used when the automotive is running normally, if the automotive does not run and was parked for days or weeks in a very harsh environment, such as a high tide, a highly corrosive environment. Then humidity or corrosive gas may enter the interior of electronic products through plastic or atmospheric compensation components. Then the humidity will also have a significant impact on the surface and internal structure of the PCB, causing it to fail. So let’s understand some details of PCB failure caused by temperature, humidity and bias (THB).

The image below shows the growth of conductive crystals during PCB condensation (water condensation)

Even if there is no condensation, high humidity can cause an electrical short if no strict materials are used. Surface Insulation Resistance (SIR) can drop, potentially causing electronics to fail. EASHUB’s method is to thoroughly understand the temperature and humidity conditions inside the protective cover (metal or plastic case) through simulation and experimental testing.

On the other hand, EASHUB tests the materials used (such as PCBs, devices, fluxes, thermal interface materials, or conformal coatings) and designs elements under different temperature and humidity conditions according to the SIR test method in IPC-9202.

EASHUB uses an efficient simulation model to predict the actual condition of local humidity in the ECU,

We determined the SIR of material and design within an enclosed enclosure under the harshest conditions.

To ensure that the PCB design elements and materials are safe and reliable, thus ensuring the reliability of the automotive PCB during the life cycle.

THB testing must take into account the CAF migration of the PCB. CAF usually occurs between adjacent lines or adjacent layers, vias, between vias and lines, causing insulation degradation or even short circuits. The corresponding insulation resistance depends on the distance between vias, lines and layers.

Common PCB technology for Manufacturing of Automotive PCBs

High-frequency substrate

The car’s predictive braking safety system and anti-collision system are the first line of defense for our safety assurance. Its electronic system is like a radar monitoring system. The automotive PCB of this part of the electronic system is mainly used to transmit high-frequency microwave signals. Therefore, in addition to the substrate material PTFE, it is also necessary to use a substrate with low dielectric loss. Unlike FR4 materials, PTFE or similar high-frequency matrix materials require special drilling speeds and feed rates during the drilling process.

Thick copper Techonology

As automobiles are developing towards smaller size and higher dynamic performance, automobiles need to use higher-tech power transmission systems and more complex electronic systems. Automotive PCBs have higher thermal performance and can withstand larger current surges.

Double-layer thick copper PCBs are relatively easy to make. However, multilayer thick copper PCBs are much more difficult to make due to the complexity of thick copper image etching and thick vacancy filling processes.

The internal paths of the multilayer thick copper PCB are all thick copper, so the pattern transfer photo dry film is also relatively thick and requires very high etching resistance. Because the etching time of the thick copper pattern becomes longer, the etching equipment and technology are also more demanding to ensure the complete wiring of the thick copper.

When we do external thick copper wiring fabrication, the combination between laminating a relatively thick copper foil and patterning a thick copper layer can be done first, followed by film void etching. In addition, the anti-plating dry film of pattern plating also needs to be relatively thick.

In addition to the above difficulties, we also encounter the following problems:

• The surface difference between the inner conductor of the multilayer thick copper PCB and the insulating substrate material is large.
• Ordinary multilayer board lamination cannot be completely filled with resin, and it will generate cavities.

To solve this problem, we should use thin prepregs with high resin content as much as possible. If the copper thickness of the internal routing on some multilayer PCBs is not uniform, we can use different prepregs in areas with large or small differences in copper thickness.

HDI technology

The comfort and good experience of the car are also closely related to the entertainment and communication systems built into the car. Automotive built-in entertainment microcomputers often use HDI PCBs.

HDI PCB technology includes micro-hole drilling and electroplating, lamination positioning and other processes. Due to the rapid development of automotive technology, more and more common applications in life are built into automotive systems. Therefore, with the increase in automotive electronic systems, more PCBs are bound to be used to meet the requirements of high-quality cars better.

Component embedding

In order to reduce the size of components, the assembly density of the PCB must be increased. PCBs with embedded components are widely used not only in mobile phones but also in automotive electronics.

According to different component embedding methods, the manufacturing methods of component embedded PCBs are also different. There are mainly four manufacturing methods for component embedded PCBs used in automotive electronic systems:

• Excavation type
• Lamination type
• Ceramic type
• Module type

The above is the supply technology commonly used in manufacturing automotive PCBs, so how to choose a reliable automotive PCB manufacturer.