Alfalight Product Qualification Methodology
Qualification of a semiconductor laser diode product involves reliability testing of the chip and package. It also requires product performance over multiple manufacturing lots. Alfalight has two product qualification designations: industrial and telecom. The telecom product qualification designation is sometimes referred to as a "Telcordia level" qualification. Upon completion of qualification testing and manufacturing performance characterization over a minimum of 3 separate work orders, the part is released to production. These products are assigned an "A" prefix to the product name. In the course of the New Product Introduction (NPI) project and prior to full release to production, Alfalight may opt for a limited release to selected customers to enable early design-ins and characterization. These products are then given an "X" prefix. The "X" prefix is temporary and the product is eventually expected to achieve "A" status.
Chip level reliability testing
Semiconductor laser diode device failures can occur due to bulk defects or facet damage. It is beyond the scope of this note to provide a detailed explanation of the failure modes. Alfalight uses proprietary epitaxial processing and facet treatment along with careful materials engineering to minimize bulk and facet failures.
Failure hazard rates follow the familiar bath-tub curve. It is the goal of the manufacturing process to eliminate the initial ("infant mortality") failures by use of good process controls and accelerated burn-in. Beyond the infant mortality phase, failures during operation can be modeled by a lognormal or Weibull distribution with acceleration parameters of temperature, facet power and current. For a given device configuration, the power and current may be collapsed into a single variable. The acceleration is modeled as a power law for power and Arrhenius equation for temperature. To extract the lognormal (or Weibull) distribution parameters along with the power law and Arrhenius constants, a multi-cell matrix of units is run through life-testing. A typical life-test consists of five cells as shown below. The junction temperature is estimated from knowing the case temperature and the submount thermal impedance.
The "accelerated life-testing" powers and temperatures are deliberately chosen to be significantly higher than operating conditions. The life-testing continues for >5,000 hours or until all units in the cell fail. Failures are expected and in fact, necessary for model parametric extraction. After failure modeling is completed with a good fit to the data and failure analysis is performed, the product engineer is able to predict field performance for a given set of operating power ("Pop") and temperature ("Top") conditions.
Package level reliability testing
Alfalight provides two kinds package families: (a) "Chip on Submount" – designated by letters: Q, C and P mounts and (b) "Fiber coupled" – designated by pin count: 6-pin and 14-pin packages. Again, a detailed explanation of package induced failures is beyond the scope of this note. Alfalight uses proprietary solder hierarchy schemes along with well characterized fiber attach processes performed on custom equipment to provide world class performance and reliability. Package testing involves performing a series of standardized environmental tests. Unlike chip level testing, a successful package reliability test would have zero failures.
The following suite of tests is performed during package reliability testing:
1. High temperature operation2. High temperature storage
3. Low temperature storage
4. Temperature cycling
5. Accelerated aging temperature cycling
6. Damp heat
7. Mechanical shock and vibe
8. Thermal shock
9. Fiber integrity tests: twist, side-pull, cable retention
10. Internal moisture
11. Hermeticity
12. ESD
13. Flammability
14. Die shear
15. Solderability
16. Wire-bond strength
"Industrial" Product Designation
Alfalight's industrial products have demonstrated >20,000 hours MTTF (mean time to failure) at standard operating conditions. A single chip life-test cell should show 0/8 fails after 2,500 hours at operating power and Tcase=70°C. All package testing should be completed with zero failures. Burn-in conditions should be equivalent to the first 1000 hours of standard operation.
"Telecom" Product Designation
Alfalight's industrial products have demonstrated a FIT rate <450 at standard operating conditions. All package testing will pass Telcordia GR-468-CORE requirements. Any level 2 QS9000 change or above will require customer approval. Burn-in conditions should be equivalent to the first 2500 hours of standard operation.
Alfalight's device, package and Telcordia qualification reports are available to our partners and customers upon request.
