Introduction to optocouplers

An optocoupler (OC) is an isolation device that uses an optical signal to convert electrical to optical and back to electrical energy. It usually contains a light emitting diode as the light source and a photosensitive semiconductor device as the receiver.

With their small size, excellent electrical isolation and strong immunity to interference, optocouplers hold an important place in many electronic applications. They are increasingly used in automotive electronic systems in particular, so they must meet the industry's strict reliability standards before they can be used in vehicle manufacturing. Automotive optocouplers must therefore pass AEC-Q series certification.

Schematic of an optocoupler circuit. Note: the photosensitive semiconductor device referred to below is the component on the receiving side.

Automotive certification standards for optocouplers

The 2013 version of AEC-Q101 included forward and reverse operating tests and applied to optoelectronic devices. In 2017 AEC-Q102 was published, providing a basis for certifying optical devices. In 2020 the A revision of AEC-Q102 was published, indicating that optocouplers and other optical assemblies would be further subdivided in AEC-Q102-003. In 2021 AEC-Q101 was updated to Revision E, removing the description of optical devices and their related environmental stress and life tests.

At the end of 2022 AEC-Q102-003 was published, formally listing optocouplers as one type of OE-MCM and confirming AEC-Q102-003 as the automotive standard for optocouplers.

AEC-Q102-003 applies to category B of OE-MCM (source: AEC-Q102-003, Rev. 28 August 2022)

Description of optical devices in AEC-Q101 and AEC-Q102

Comparison of AEC-Q101 and AEC-Q102

Similarities and differences between AEC-Q102 and AEC-Q101

1. Scope. AEC-Q101 covers automotive discrete semiconductor components such as transistors, diodes and optical devices. AEC-Q102 focuses on automotive discrete optoelectronic semiconductor components such as LEDs, laser components, photodiodes and phototransistors.

2. Sample size and environmental stress testing. AEC-Q101 requires 3 lots of 77 pieces with LTPD 1, giving a 1 percent failure rate at 90 percent confidence. AEC-Q102 requires 3 lots of 26 pieces with LTPD 3, giving a 3 percent failure rate at 90 percent confidence.

3. Failure criteria. Both standards treat a device as failed if its electrical and optical parameters fall outside the datasheet, if parameters change beyond the specified percentage before and after environmental testing, or if environmental testing causes physical damage.

4. Environmental stress and life testing. Both standards include high temperature operating life (HTOL), temperature cycling (TC) and power temperature cycling (WHTOL) among other tests.

5. Items added in AEC-Q102. Compared with AEC-Q101, AEC-Q102 adds vibration, shock, variable frequency vibration (VVF), mechanical shock (MS), pulsed operating life (PLT), dew condensation (DEW), hydrogen sulphide corrosion (H2S) and mixed flowing gas corrosion (FMG).

Items added in AEC-Q102 compared with AEC-Q101

1. Vibration and shock. The VVF variable frequency vibration test applies a displacement amplitude of 1.5 mm peak to peak over 20 to 100 Hz and an acceleration of 200 m/s² over 100 Hz to 2 kHz. The MS mechanical shock test applies 5 shocks in each of the six directions of the X, Y and Z axes, 30 shocks in total, with a half sine pulse of 0.5 ms duration and 1500 g peak acceleration.

2. Pulsed operating life (PLT). Pulse width 100 µs, duty cycle 3 percent.

3. Dew condensation (DEW). Temperature cycles from 30℃ to 65℃, holding at 65℃ for 4 to 8 hours, with transfer times of 2 to 4 hours and RH of 90 to 98 percent. The minimum drive current in the datasheet is maintained for 1008 hours. If no rated minimum current is defined, a drive current may be selected that does not raise junction temperature by more than 3 K.

4. Hydrogen sulphide and mixed gas corrosion. H2S corrosion holds the sample at 40℃ and 90 percent RH for 336 hours with an H2S concentration of 15 × 10^-6. FMG mixed gas corrosion holds the sample at 25℃ and 75 percent RH for 500 hours with H2S at 10 × 10^-9, SO2 at 200 × 10^-9, NO2 at 200 × 10^-9 and Cl2 at 10 × 10^-9.

What AEC-Q102 and AEC-Q101 have in common

· A product may only claim AEC-Q certification if it passes all the corresponding test items required by AEC-Q.
· A supplier may, with user agreement, use sample sizes and test conditions below AEC-Q requirements, but this cannot be regarded as AEC-Q certification.
· For ESD, a supplier may claim that a product meets the corresponding AEC-Q class, for example AEC-Q102 qualified to ESD H1B.
· Generic data is encouraged to simplify qualification and requalification, but must be based on the same process, materials and location. PV and ESD must be measured and may not use generic data. The user has the final say on whether generic data may replace specific measured data.
· Order of precedence: where documents conflict, the order is purchase order, specially agreed product requirements, AEC-Q requirements, reference standards cited by AEC-Q, and supplier product datasheet.
· All qualification samples must be manufactured at the production site, that is the lot location.
· Requalification is required whenever a change to any device affects or may affect its construction, mounting, function, quality or reliability.
· For every qualification the supplier must provide the user with a certificate of design, construction and qualification (CDCQ).

Items common to AEC-Q102 and AEC-Q101

Preconditioning, visual inspection, parameter verification, ESD, physical dimension checks, terminal strength, resistance to soldering heat, solderability, wire pull, solder joint push, die shear and lead-free requirements.

Conclusion

Although AEC-Q102 and AEC-Q101 share certain requirements, AEC-Q102 provides more detailed qualification guidance for optoelectronic devices such as optocouplers, including additional vibration and shock tests. Choosing the correct certification standard is essential to ensuring the high reliability of optocoupler products.