DC/DC converters are now common in automotive applications at a range of power levels. Parts must comply with AEC-Q standards for quality and stress tests and automotive customers may also require additional features such as ‘inspectable’ solder joints. This article discusses the issue and the solutions available.
mobile data center
It has been said that the modern car is a mobile data center, and EVs add in industrial-scale electrical power handling, battery charging, and motor drives that are rated in fractions of a megawatt.
In a modern car, there are upwards of 100 Microprocessors and controllers operating in the background, handling everything from wireless connectivity, to heated seats, to the implementation of complex algorithms for three-phase control of the traction motors to squeeze out the best efficiency and range.
PoL converters
As in data centers, power bus architectures have been devised in cars to minimize losses
All these electronics need their power rails and these derive from the battery, whether a 12V/24V lead-acid type or a lithium-ion pack at up to 800V. As in data centers, power bus architectures have been devised in cars to minimize losses and particularly weight, and DC/DC converters are an integral component to provide the voltage conversion stages from battery to end load.
Among these DC/DCs, non-isolated Point-of Load (PoL) converters are fitted close to each sub-system and processor to give the best regulation and dynamic performance exactly where it is needed. Other DC/DCs such as LED drivers are also common.
Automotive DC/DCs need AEC-Q qualification
A web search will show PoLs and LED drivers as being one of the most ubiquitous types of DC/DC converters with a wide variety of features and ratings.
However, in the automotive application, the choice has to narrow to types with the right qualification, defined by the Automotive Electronics Council, (AEC) founded by Chrysler, Ford Motors, and Delco Electronics, who set standards for stress testing, qualification, and production quality control of components in the automotive arena.
referenced standards
In all cases, standards from other sources such as MIL-STD-883, JEDEC, JESD, IPC, and UL are referenced
The standards are designated AEC-Qxx and currently relate to stress testing of ICs (AEC-Q100), discrete semiconductors, (AEC-Q101), optoelectronics, (AEC-Q102), sensors (AEC-Q103) and ‘multi-chip modules’ (AEC-Q104).
Passive components are covered by a range of standards in the AEC-Q200-xxx series and in all cases, standards from other sources such as MIL-STD-883, JEDEC, JESD, IPC, and UL are referenced.
AEC-Q standards
Component manufacturers ‘self-certify’ that they meet the AEC-Q standards but they are a ‘base’ level, and further requirements will be set by the automotive customer at any tier, for their particular application.
At a minimum, this will define the area of the vehicle where the part is used with its environmental conditions defined. For example, ambient operating temperature is defined for different areas for ICs in Table 1.
TS/IATF 16949:2016 certification
There is a strong emphasis in the AEC-Q standards on the ability of a supplier to maintain stress tolerance
As a separate requirement, a component supplier to the automotive industry must have a quality system with TS/IATF 16949:2016 certification, a step up from the commonly used ISO 9001:2015.
There is a strong emphasis in the AEC-Q standards on the ability of a supplier to maintain the stress tolerance of components in their real manufacturing process. Although the AEC-Q stress tests need only be done once, parts must be used that have been fabricated using production tooling, processes, and operatives, using non-consecutive lots.
Product Part Approval Process (PPAP)
If anything in the component or manufacturing process changes, requalification is necessary using a Product Part Approval Process (PPAP). This was determined by the Automotive Industry Action Group and the PPAP has its levels of applicability ranging from 1 to 5 with increasing requirements for supporting data and sample submission as shown in Table 2.
PPAP is part of an over-arching requirement of Advanced Product Quality Planning (APQP) which includes comprehensive documentation of the manufacturing process, test records, and design/process failure mode and effect analysis (FMEA).
Component solder joints must be ‘inspectable’
The evolution of ICs away from ‘gull-wing’ styles to chip-scale packaging, where the terminations can be ball grid or land grid
Automotive customers have their in-house standards and preferences and one that is common is to require components to have their solder joints ‘inspectable’. This comes from the evolution of ICs away from ‘gull-wing’ styles to chip-scale packaging, where the terminations can be ball grid or land grid arrays, for example.
These styles save significant board space and enhance thermal and electrical performance, but the solder joints, formed by reflow methods, are hidden and cannot be verified as good by ‘Automated Optical Inspection’ (AOI). X-ray analysis can be used and although production-line systems are possible, this is expensive, slow, and must be performed in a safe, screened chamber.
land-grid type packages
For some land-grid type packages such as the Quad Flat No-lead (QFN), which are quite common for power devices such as PoL DC/DC converters, the relatively few terminations can be brought out to the edge of the device as part of an internal lead frame.
This makes the connection visible, but the action of mechanically singulating the devices from the external lead frame leaves edges with bare alloy which are not guaranteed to ‘wet’ during the reflow process and show a good joint on inspection, even though the tinned pad may be making a perfect connection under the device.
‘wettable’ flanks
The cut edges cannot be easily re-plated as they may all be electrically isolated after singulation.
A solution to achieve ‘wettable’ flanks that are visible in AOI, is to form a step in the molding and leadframe which is tin-plated with the other surfaces when the leadframe is whole, but is not cut by the singulation process and allows a good joint to be visible and verified (Figure 1).
QFN DC/DCs with wettable flanks are available
Examples of products with wettable flanks recently introduced by RECOM are their RPX-0.5Q/1.5Q PoL DC/DCs and their RPY-1.5Q LED driver, Figure 2.
The RPX-xx-Q parts are upgrades to RECOM’s existing popular RPX series DC/DCs to include solder-inspectable flanks, standard on the RPX-0.5Q with 0.5A output and optional on the RPX-1.5Q with 1.5A output.
AEC-Q100 Grade 1
Both DC/DCs are in the same low-profile 3 x 5mm thermally-enhanced QFN package
The parts have been certified to automotive AEC-Q100 Grade 1 requirements, passing all of the AEC-Q stress tests under the specified environmental conditions and operating to 125°C with appropriate derating, depending on input/output voltage combination.
Both DC/DCs are in the same low-profile 3 x 5mm thermally-enhanced QFN package and operate over an input range of 4 – 36VDC with their output programmable from 0.8 – 30VDC (34V for the RPX-0.5Q).
‘3D packaging’ technology
The DC/DCs feature RECOM’s ‘3D packaging’ technology with an over-molded ‘Flip Chip on Leadframe’ (FCoL) construction and integrated inductor. Monitoring and control functionality includes on/off and synchronization inputs as well as a power good output.
Soft start, along with full short circuit, over-current, over-temperature, and input under-voltage protection is provided.
Input and efficiency
RPY-1.5Q is fully protected against over-temperature, short circuits, input under-voltage, and output over current
The RPY-1.5Q LED driver from RECOM is also AEC-Q100 certified with optional wettable flanks. The part is in the same QFN package as the RPX series and is rated for up to 1.5A constant current for high-power LED driving and lower values of current can be set with a simple resistor network.
Input is 4 – 36VDC and efficiency is particularly high at 95% typical. 0-100% dimming can be achieved by a digital PWM signal to a pin on the device or through analog voltage control. The same pin also acts as a shutdown input. The RPY-1.5Q is fully protected against over-temperature, short circuits, input under-voltage, and output over current and a fault indicator pin signals thermal shutdown or LED open/short conditions.
testing and quality control
The ability to optically inspect solder joints of QFN and similar packages, required by automotive customers, is a feature that will be welcomed in other industries.
The extensive testing and quality control of AEC-Q-certified power products by manufacturers holding ISO/IATF 16949 quality certification will also give extra confidence in parts designed for critical application areas such as industry, data centers, and medical.
