Considerations for Automotive-Grade Resistors
This article explores the idea of automotive-grade components and some of the common criteria and standards that companies use to justify their automotive-grade labels.
The growing demand for USB ports, infotainment systems, sensing wipers, adaptive cruise control, blind-spot detection, and other advanced driver-assisted systems have created consistent and rapid growth in the automotive electronics market.
Figure 1. The automotive market is incorporating more and more electronics, encouraging the demand for automotive-grade parts.
The global automotive electronics market size was more than $245B in 2019 and is projected to be more than $330B by 2022. The demand from automotive electronic producers was largely responsible for the 2018 SMD resistor and capacitor shortage. The rising demand for electronic components and the risk of shortages lead engineers to add multiple sources on the resistor AVLs, but how does an engineer select a quality part that meets the needs of the application? A logical starting point is for the engineer to select parts that are labeled as "automotive-grade.”
To capitalize on this rapidly growing market, many suppliers tout their parts as automotive-grade. Yet a quick comparison of a supplier’s general-purpose resistor versus its automotive-grade equivalent provides no help; the parts appear to be identical (see Figure 2).
Figure 2. Side by side comparison of a supplier's general-purpose thick film resistor versus the same supplier's automotive-grade version
So, what does “automotive-grade” really mean? Unfortunately, there is no single, concise answer. Automotive-grade is defined differently by different manufacturers. In addition, the automotive electronic market has expanded so much that there are more applications within this segment than ever before. The purpose of this article is to explore some of the common criteria that suppliers and customers use to justify their automotive-grade labels.
Sulfur Effect Mitigation
Over 20 years ago, one of the major concerns that arose in the automotive electronics segment was sulfur contamination. Sulfur is released into the atmosphere from multiple sources such as hoses and gaskets used in “under the hood” applications as well as upholstery and carpeting in the cabin. Over time, this free sulfur can react with silver found in the inner terminations of various types of resistors, forming silver sulfide. Silver sulfide is not conductive, so continued growth along the interface between the termination and the resistor element may cause the resistor to electrically open.
Resistor manufacturers have developed several methods to counter the effects of sulfur, including the use of different materials such as the addition of palladium to the silver conductive paste, different termination designs, and other manufacturing techniques. Also, several procedures have been developed to test the resistance of component designs to the effects of sulfur.
The first was an adaptation of ASTM B809-95, but this standard was not meant to be applied to electronic components, so there were no true industry standard acceptance criteria for this test. A committee of the ECIA (Electronic Components Industry Association) then developed a true industry-standard test procedure with component pass/fail criteria, ANSI/EIA-977. This test standard is now more commonly used.
As automotive electronics continued to grow, more quality standards have been introduced to ensure the quality of products used in these applications. Production Part Approval Process (PPAP) was created to standardize the approval process. Some automotive customers require parts to be tested to PPAP of the appropriate level and be produced in a certified factory, typically to IATF16949. What are PPAP and IATF16949?
Production Part Approval Process (PPAP)
The PPAP is a standardized process used in the automotive industry to help manufacturers and suppliers qualify parts. There are 18 elements to the PPAP and customers may require different levels of PPAP. The summary of the results is called a Part Submission Warranty. There are five (5) levels of PPAP:
- Level 1 – Part Submission Warrant (PSW) only submitted to the customer
- Level 2 – PSW with product samples and limited supporting data
- Level 3 – PSW with product samples and complete supporting data
- Level 4 – PSW and other requirements as defined by the customer
- Level 5 – PSW with product samples and complete supporting data available for review at the supplier’s manufacturing location
The IATF 16949 is an internationally recognized quality management system standard specific to the automotive industry. This standard consists of all the ISO 9001:2015 requirements plus additional automotive specific requirements.
With improved manufacturing processes and more electronics being used in non-critical applications, new standards have emerged to help engineers find reliable solutions. The most common is AEC-Q200.
AEC-Q200 is a global standard for qualification stress testing that passive electronic components must meet if they are intended to be used in automotive applications. Parts are “AEC-Q200 qualified” if they pass each of the tests making up the AEC-Q200 standard. Each test specifies a minimum sample size based on the nature of the testing. These tests are conducted by the supplier and the data and reporting are maintained by the supplier which is sent to customers as requested.
Factory Established Standards
Although the AEC-Q200 standard has become the de facto standard for most automotive applications, there are still some applications and customers that require higher standards. Some suppliers have developed their own criteria for “automotive grade". In these cases, the supplier specifies its own standards and provides data and supporting documentation to the customer to verify its claims. For example, in addition to AEC-Q200, Stackpole’s automotive-grade thick film resistors are:
- Produced on dedicated lines and equipment
- These production lines are operated exclusively by certified operators
- 100% Automated Optical Inspected (AOI)
The automotive electronics market will continue to grow. It is imperative that engineers find reliable components that meet the demands of the various applications. The above information highlights some of the common standards and certifications that exist in the resistor market. When selecting a resistor for an automotive application, an engineer needs to understand how the supplier is defining “automotive-grade” to ensure the right part is used for the design.