Enter Supply Chain of AI Smart Car in Five Steps of International Auto Reliability Specs

PCBs bridge active and passive components. You may rework failed components but not replace any PCB after all its components are removed. A PCB is, in essence, the key electronic automotive component.

Automotive PCBs are most likely validated according to IPC-6012 rather than any exclusive validation method. The IPC-6012DA, the first automotive specific PCB validation and acceptance specification by IPC in 2016, is the first step by IPC to regulate PCB makers competing in this fast growing market. It includes Thermal shock endurance testing, High temperature endurance testing, Humidity storage testing, Conductive anodic filament testing (CAF testing), Surface insulation resistance testing (SIR testing) and so on. This standard is now an important reference for brand owners and Tier 1 in PCB reliability verification.

The Board Level Reliability (BLR) is the most common global method to verify IC component solder joint reliability after being mounted on PCB. It has been a routine test item for hand-held devices; however, as more IC components are used in cars which increase the complexity of the automotive electronic system, the BLR has gradually become one of the important test items of automotive electronics.

Tier 1 module makers are making rising efforts in creating proprietary board level tests, including Bosch, Continental, and TRW, among others. More strikingly, the AEC has also come up with the latest AEC-Q104 qualification to clearly define the test items of BLR recently. Although the AEC-Q104 covers only Temperature Cycle Test (TCT), Drop Test, Low Temperature Storage Life (LTSL) and Start-up & Temperature Steps (STEP), etc, and has not been completely close to the specification of Tier 1 makers; AEC-Q104 is treated as a big step in the BLR general standard. See following table for the testing conditions of Board level required by Tier 1 module makers.

1. The top five solder joint failure types suffered by board level automotive chips found in iST and DEKRA iST labs:

(1) Solder joint size and layout
(2) Solder joint alloy ingredients
(3) PCB design mechanism and material selection
(4) Reflow temperature and flux residual
(5) Underfill material surrounding solder joint (see figure 2)

The aforementioned failures (2), (3), and (5) may be influenced by thermal expansion coefficients, which, in turn, may lead to different deformation levels as automotive chips are most likely operating in very high temperatures. In addition to the aforementioned vibration stress, the repetitive contraction and expansion due to changing temperatures may pull and press solder joints and break them. Selecting chip materials with closer thermal expansion coefficients can reduce temperature-related stress greatly. Most consumer goods like computers and cellphones enjoy warranty periods of around 2-5 years while the life cycles of automotive chips may last 10-20 years. This requires carefully designed test conditions and early adoption of these factors in initial chip development. Far more stringent safety and reliability requirements in the automotive industry over computer and mobile phone products not only extend the service life of chips but also improve remedy schedules and costs after failure analysis.

2.Do BLR test conditions of consumer electronics remain applicable to automotive electronics?
This is one of questions most frequently asked by our customers, and the answer is “No”. These conditions no longer apply as the operation environment and structure of car borne platform differs. Chips employed in-vehicle are constantly subject to vibration, mechanic stress and poor external conditions especially when cars are running. A product’s qualified consumer electronics requirements may fail early in practical operation environment.

Take the vibration test; handheld products are most likely subject to simulated ordinary land, sea, and air shipment conditions while the vehicle ones shall pay more attention to temperature and humidity durability and resistance against temperature and vibration due to long time exposure to external environment. Environment at Frigid Zone and Tropical Zone differs; temperature of confined space under direct sunlight may hit 100°C or even 150°C measured close to engine. To better mimic the real operation environment the factor of vibration is added in the test environment. That is, the combined vibration test known to us. Besides vibration and temperature test, the solder joints should subject to such as push, pull and cyclic bending test to ensure the strength of it is safe to the rider.

The RoHS implemented by the EU in July 2006 requires that the Pb content in electronic products shall be less than 1000ppm. Replacing the tin-lead solder process for electronic products, in use for more than half a decade, with a Pb-free process mandates a whole new review and validation process for equipment, test methods, product quality and reliability, among others. The melting point of Pb-free material rose to 217℃ from the 183℃ melting point of tin-lead material, which, in turn, results in hardening, and brittle solder joints with poor fatigue resistance. Process yield becomes very hard to improve as a result of tin whiskers caused by solder joint flaws. This hampers its adoption in the medical, defense, and automotive industries when compared with its adoption in the consumer electronics industry due to the extremely high demands on reliability.

The AEC-Q100 Version G released in 2007 came without Pb-free validation requirements. It was addressed in the Q005 (PB-FREE TEST REQUIREMENTS) written by the AEC in 2009, and version H of AEC-Q100 in 2014 finally had Pb-free validation tests, including Solderability, Solder heat resistance, and Whisker. The automotive industry eventually marched into the era of environmental protection.

Thanks to lessons learned in implementing a Pb-free process for consumer electronics products, manufacturers are better equipped in managing the challenges of Pb-free and adapting it into the automotive phase. See figure 3 for a Pb-free validation flowchart. (courtesy of DEKRA iST Lab)

Furthering the Pb-free process for on-board information systems, the iST and DEKRA iST Lab where this author is now working has been consigned the validation of ABS and SRS safety function-critical ECU by international Tier 1 brand owners. This without a doubt marks that the automotive industry, which mandates the highest level of reliability, is adding the Pb-free process into its core personal safety electronic components.

The experiences of the iST and DEKRA iST Lab in working by Tier 1 tells that different areas may impose different requirements:

1. Western automotive makers and Tier 1 owners pay more attention to product service life, set up test programs in terms of product life cycle, and accelerated tests including Arrhenius Model for thermal aging, Hallberg-Peck Model for high temperature and humidity and Coffin-Manson Model for temperature cycling.
2. American manufacturers especially demand High Accelerated Life Testing (HALT) and aim to identify design flaws with Test to Failure. The goal is to improve design flaws at the design validation phase as shown in figure 4.
3. Asian countries (Japan and South Korea) require ion migration and whisker validation. My educated guess suggests most of these electrochemical validations in Asia are made by long hours rather than accelerated testing. Products of Asian and Tier 1 makers subject to these tests may lend the impression that the actual products will have a longer automotive electronic product life cycle compared to those by western brands who put more effort into environment protection.

System module validation requirements may come at three stages:

1. Rivalry: the company is faced with a live-or-die challenge and the immediate and only goal is to survive by launching products on the fastest timeline and at the lowest costs. There is nothing left to say about responsibility and quality.
2. Alternative brand: the company is well established and is aiming to build up brand value. Quality verification is most likely subject to global automotive specifications, which almost always comes to the most widely adopted in the industry, ISO 16750 (Traditional Chinese edition CNS 15481, Simplified Chinese edition GB/T 28046 and Japanese edition JASO D014). There are four validations covered by it: electrical load, mechanical load, climate load, and chemical solvent load.
3. Components for brand owner: there are no other options except being certified by the specification of the car maker or of Tier 1