Reliability Stress Test Descriptions

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1. Solder Reflow Preconditioning (PRECON): The preconditioning stress

sequence is performed for the purpose of evaluating the capability of semiconductor devices to withstand the stresses imposed by a user’s printed circuit board assembly operation. A properly designed device (i.e. die and package combination) should survive this preconditioning sequence with no measurable changes in electrical performance. Furthermore, preconditioning of properly designed devices should not produce latent defects which lead to degraded reliability during life or environmental stress tests. Changes in electrical characteristics and both observable as well as latent physical damage during this stress sequence result principally from mechanical and thermal stresses and from ingress of flux and cleaning agents. Effects include die and package cracks, fractured wire bonds, package and leadframe delamination, and corrosion of die metallization.

Stress Conditions:

Step Stress Conditions

1 Initial Electrical Test Room temperature 2 External Visual Inspection 40X Magnification

3 Temperature Cycling 5 cycles at –40°C (max) to +60°C (min) (Step is optional)

4 Bake Out 24 hrs (min) at 125°C

5 Moisture Soak Per MSL rating

6 Reflow 3 cycles per referenced profile

7 Flux Application 10 sec immersion in water soluble flux @ room temp

8 Cleaning Multiple DI water rinses

9 Dry Room temperature

10 Final Electrical Test Room temperature Reference Industry Standard: JESD22-A113

2. Operating Life (SOPL/DOPL): The operating life test is performed for the purpose of demonstrating the quality and reliability of devices subjected to the specified conditions over an extended time period. Either a static or dynamic condition may be used, depending on the circuit type and the wafer fabrication technology. The specified test conditions (i.e. bias conditions, loads, clock inputs, etc.) are selected so as to represent the worst case conditions for the device. Unless otherwise specified in the detailed test procedure, the test is run at an ambient temperature of +125°C or above. Many device types are routinely run at +150°C ambient. Ambient temperatures above +170°C are generally considered impractical due to the physical limitations of circuit boards, sockets, device lead finishes, molding compound glass transition temperatures, etc.

Stress Conditions: 125°C – 150°C, Bias

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3. Power Cycle (PRCL): The power cycle test is performed to determine the effects on solid state devices of thousands of power-on/power-off operations such as would be encountered in an automobile or a TV set. The repetitive heating/cooling effect caused by multiple on/off cycles can lead to fatigue cracks and other degrading thermal and/or electrical changes in devices which generate significant internal thermal heating under maximum load conditions (i.e. voltage regulators or high-current drivers). This test forces junction temperature excursions at the rate of ~ 30 cycles per hour (typical for small packages).

Stress Conditions: ∆Tj = 100°C or 125°C, on/off cycle dependent on package size: Package Size Classification

Package Volume (mm3) <350 350 - 2000 >2000 P a c k a g e T h ic k n e s

s <1.6 mm SMALL SMALL SMALL

1.6 mm - 2.5 mm SMALL MEDIUM LARGE

>2.5 mm MEDIUM LARGE LARGE

On/Off Time

Number of Cycles Required

Reference Industry Standard: JESD22-A122

∆TJ = 100°C ∆TJ = 125°C P A C K A G E S IZ E

SMALL 2 min on / 2 min off 2 min on / 2 min off MEDIUM 3.5 min on / 3.5 min off 3.5 min on / 3.5 min off

LARGE 5 min on / 5 min off 5 min on / 5 min off

∆TJ = 100°C ∆TJ = 125°C P A C K A G E S IZ E SMALL 10000 7500 MEDIUM 8572 4286 LARGE 6000 3000

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4. High Temperature Reverse Bias Test (HTRB): The HTRB test is configured to reverse bias major power handling junctions of the device samples. The devices are characteristically operated in a static operating mode at, or near, maximum-rated breakdown voltage and/or current levels. The particular bias conditions should be determined to bias the maximum number of solid state junctions in the device. The HTRB test is typically applied on power devices.

Stress Conditions: 150°C Tj, Biased

5. High Temperature Gate Bias Test (HTGB): The HTGB test biases gate or other oxides of the device samples. The devices are normally operated in a static mode at, or near, maximum-rated oxide breakdown voltage levels. The particular bias

conditions should be determined to bias the maximum number of gates in the device. The HTGB test is typically used for power devices.

Stress Conditions: 150°C Tj, Biased

6. Temperature Humidity Biased Test (THBT): The steady-state temperature-humidity-bias life test is performed for the purpose of evaluating the reliability of non-hermetic packaged devices operating in humid environments. It employs severe conditions of temperature, humidity, and bias which accelerate the penetration of moisture through the external protective material (encapsulant or seal) or along the interface between the external protective materials and the metallic conductors passing through it. When moisture reaches the surface of the die, the applied potential forms an electrolytic cell, which can corrode the aluminum, affecting DC parameters through its conduction, and eventually causes catastrophic failure by opening the metal. The presence of contaminants such as chlorine greatly

accelerates the reaction as does excessive phosphorus in the PSG layers (passivation, dielectric or field oxide).

Stress Conditions: 85%RH, 85°C

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7. Highly Accelerated Stress Test (HAST): HAST is performed for the purpose of evaluating the moisture resistance of non-hermetic packaged devices operating in high humidity environments. Bias is applied minimizing current draw using alternating potentials wherever possible. The test approximates a highly accelerated version of the THBT test. These severe conditions of pressure, humidity, and temperature, together with bias, accelerate the penetration of moisture through the external protective material (encapsulant or seal) or along the interface between the external protective material and the metallic conductors passing through it. When moisture reaches the surface of the die, the applied potential forms an electrolytic cell, which can corrode the aluminum, affecting DC parameters through its conduction, and eventually causes catastrophic failure by opening the metal. The presence of contaminants such as chlorine greatly accelerates the reaction as does excessive phosphorus in the PSG layers (passivation, dielectric or field oxide).

Care must be taken when using HAST as a stress technique for assembly packages that have mold compound and die attach materials with low Tg, since uncharacteristic failures may result.

Stress Conditions: 130°C, 85%RH, 18.6psig OR 110°C, 85%RH, 3psig Reference Industry Standard: JESD22-A110

8. Autoclave (ACLV): The autoclave (or pressure cooker) test is performed for the purpose of evaluating the moisture resistance of non-hermetic packaged devices. No bias is applied to the devices during this test. It employs severe conditions of

pressure, humidity and temperature not typical of actual operating environments that accelerate the penetration of moisture through the external protective material

(encapsulant or seal) or along the interface between the external protective material and the metallic conductors passing through it. When moisture reaches the surface of the die, reactive agents cause leakage paths on the surface of the die and corrode the die metallization, affecting DC parameters and eventually catastrophic failure. Other die-related failure mechanisms are activated by this method including mobile ionic contamination and various temperature and moisture related phenomena. The autoclave test is destructive and produces increasing failure rates when repetitively applied. It is useful for short-term, comparative evaluations such as lot acceptance, process monitors and robustness characterization but generates no absolute information since accelerating factors relating to the operating environment are not well established. In addition, the autoclave test can produce spurious failures not representative of device reliability, due to excessive chamber contaminants. This condition is usually evidenced by severe external package degradation, including corroded device terminals/leads or the formation of conducting matter between the terminals, or both. The autoclave test is therefore not suitable for measurements of package quality or reliability.

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ACLV test is not required in the qualification of standard Fairchild products. However, during the development stages of a package ACLV can be used to understand inherent weakness in the technology. Cautions must be taken when interpreting results because failure mechanisms may be due to exceeding the capabilities of the package, producing unrealistic material failures. ACLV may be a required test for some customers or markets, such as the automotive market. Stress Conditions: 100%RH, 121°C, 15psig

9. Temperature Cycle (TMCL): The temperature cycle test is conducted for the purpose of determining the resistance of devices to alternating exposures at extremes of high and low temperatures. Permanent changes in electrical

characteristics and physical damage produced during temperature cycling result principally from mechanical stress caused by thermal expansion and contraction. Effects of temperature cycling include cracking and delamination of packages,

cracking or cratering of die, cracking of passivation, delamination of metallization, and various other changes in the electrical characteristics resulting from

thermo-mechanically induced damage.

Stress Conditions: Various. -40°C to +125°C or –65°C to +150°C are typical. Reference Industry Standard: JESD22-A104

10. Board Level Temperature Cycle (BTMCL): The BTMCL test is intended to provide fatigue-related wearout information on the solder joint attachment of devices to circuit boards. Daisy chain structure test devices are mounted to circuit boards and cycled through temperature extremes typically in the range of 0°C to +100°C. During stress, the solder joint resistance is continuously monitored and a unit is considering failing when 5 cumulative incidences of elevated resistance (> 1000 ohms) are detected. Ideally, testing should continue until a cumulative 63% failure rate of the test sample has been observed.

Stress Conditions: 0°C to +100°C, 2 cycles/hour Reference Industry Standard: IPC-SM-785

11. High Temperature Storage Life (HTSL): The high temperature storage (also called the stabilization bake test) is employed for the purpose of determining the effects of storing devices at elevated temperatures without electrical stresses applied. It is also a useful test for determining the long term reliability of wire bonds which are susceptible to formation of intermetallic voids (such as gold wire bonds on aluminum bond pads).

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Devices under test are subjected to continuous storage in a chamber with circulated air heated to +150°C. At the end of the specified stress period, the devices are removed from the chamber, allowed to cool, and electrically tested. Interim measurements are made if specified in the detailed test procedure.

Stress Conditions: 150°C or 175°C

12. Reflow Moisture Sensitivity (MSL): The purpose of this stress is to classify the sensitivity of non-hermetic solid state Surface Mount Devices (SMDs) to moisture-induced stress so that they can be properly packaged, stored, and handled to avoid subsequent thermal/mechanical damage during the assembly solder reflow

attachment and/or repair operation. Stress Conditions:

1 Initial Electrical Test Per data sheet 2 External Visual Inspection 40X Magnification

3 CSAM Inspection Classify and Measure Initial Delamination Levels

5 Moisture Soak Per Target MSL rating

6 Reflow 3 cycles per referenced profile

7 External Visual Inspection 40X Magnification

8 Final Electrical Test Per data sheet

9 CSAM Inspection Classify and Measure Final Delamination Levels 10 Final Electrical Test Room temperature

Reference Industry Standard: J-STD-020

13. Resistance to Solder Heat (RSDH): The resistance to solder heat test is intended to determine whether devices can withstand the effects of the heat to which they will be subjected during soldering of their terminations. The heat can be

conducted through the termination into the device package, radiated from the solder bath to the body of the device, or through direct contact with the solder wave. In order to establish a standard test procedure for the most reproducible method, the solder dip method is used because of its more controllable conditions.

During this procedure, through hole devices under test have their leads immersed in a solder bath heated to 260°C (SnPb processing) or 270°C (Pb-free processing) for a duration of 10 seconds. The devices are then cooled and tested. Endpoint

measurements include electrical testing as well as visual inspection for mechanical damage such as cracks, etc.

Small surface mount products (typically those with packages < 5.5mm x 12.5mm and DAP < 2.5mm x 3.5mm) must be fully submerged in the solder bath for a minimum of 5 seconds. It is recommended to preheat the samples prior to solder immersion at a

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rate of less than 4°C/sec to a maximum preheat temperature of 140°C. Care should be taken to fully investigate any failures that occur on products that are not

preheated, as the severe shock of solder immersion without preheating can overstress the package.

Stress Conditions: 260°C, 10 seconds (through hole products in a SnPb board assembly process)

270°C, 10 seconds (through hole products in a Pb-free board assembly process)

260°C, 5 seconds (surface mount products in a SnPb board assembly process)

270°C, 5 seconds (surface mount products in a Pb-free board assembly process)

Reference Industry Standard: JESD22-B106

14. Lead Integrity: The lead integrity test provides various methods for determining the integrity of device leads, welds, and seals. For hermetic packaged devices only, this test is followed by a hermeticity test to determine any effect of the stresses applied on the seal as well as on the leads.

Devices under test are subjected to one or more mechanical stress sequences

(tension, bending, fatigue, or torque) appropriate to the type of leads on the package. Reference Industry Standard: JESD22-B105

15. Mark Permanency: The purpose of the mark permanency or resistance to solvents test is to verify that the markings on the device package will not become illegible when subjected to solvents or cleaning solutions commonly used for removing flux residue from printed circuit boards.

Devices under test are exposed to a series of solvents while the markings are

brushed with a toothbrush. The markings must not become illegible as a result of the exposure.

This test is not required for laser marked packages. Reference Industry Standard: JESD22-B107

16. Flammability: This procedure assesses the flammability of the plastic materials used in the assembly of the packaged semiconductor device. This testing is not performed internal to Fairchild Semiconductor. Instead, a certificate of compliance to the UL94-V0 test standard is required for the plastic materials used in semiconductor package. This should be obtained from the mold compound or resin supplier or from Underwriters Laboratories directly.

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Reference Industry Standard: UL94-V0

17. Solderability: The purpose of the solderability test is to determine the solderability of all external package terminations that are normally joined by a soldering operation. This determination is made on the basis of the ability of these terminations to be wetted or coated by solder. These procedures will verify that the treatment used in the manufacturing process to facilitate the soldering is satisfactory and that it has been applied to the required portion of the part which is designed to accommodate a solder connection. An accelerated aging test is included in this test method.

The referenced standard also provides optional conditions for aging and soldering for the purpose of allowing simulation of the soldering process to be used in the device applications. It provides procedures for dip and look solderability testing of through hole, axial and surface mount devices and reflow simulated use testing for surface mount packages.

Using the dip and look procedure, devices under test are first “aged” by exposure to steam for a period of 8 hours. After aging the leads of the device are fluxed and dipped in a solder bath heated to a temperature of 215°C (SnPb board assembly processing) or 245°C (Pb-free board assembly processing) for 5 seconds. Reference Industry Standard: JESD22-B102

18. Wave Solder Moisture Sensitivity (WMSL): The purpose of this stress is to classify the sensitivity of non-hermetic solid state Surface Mount Devices (SMDs) to moisture-induced stress resulting from a full immersion wave solder board mounting process so that they can be properly packaged, stored, and handled to avoid

subsequent thermal/mechanical damage during the assembly solder reflow attachment and/or repair operation.

Stress Conditions:

1 Initial Electrical Test Room temperature

2 External Visual Inspection 40X Magnification

3 CSAM Inspection Classify and Measure Initial Delamination Levels

5 Moisture Soak Per Target MSL rating

Preheat Room temp to 140°C in minimum of 80 seconds 6 Solder Immersion 1 full immersion, 10 seconds minimum

260°C for SnPb board assembly processes 270°C for Pb-free board assembly processes 7 External Visual Inspection 40X Magnification

8 Final Electrical Test Per data sheet

9 CSAM Inspection Classify and Measure Final Delamination Levels

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Reference Industry Standard: JESD22A-111

19. Solder Immersion Preconditioning (WVSLDR): The solder immersion preconditioning stress sequence is performed for the purpose of evaluating the capability of semiconductor devices to withstand the stresses imposed by a user’s waver solder printed circuit board assembly operation. In this type of board assembly process it is common for small surface mount products to be glued to the back side of a board and be completely immersed in the solder wave at the same time that the through hole parts on the top side of the boards are solder with the wave. The solder temperature will be 260°C for SnPb board assembly processes and 270°C for Pb-free board assembly processes.

A properly designed device (i.e. die and package combination) should survive this preconditioning sequence with no measurable changes in electrical performance. Furthermore, preconditioning of properly designed devices should not produce latent defects which lead to degraded reliability during life or environmental stress tests. Changes in electrical characteristics and both observable as well as latent physical damage during this stress sequence result principally from mechanical and thermal stresses and from ingress of flux and cleaning agents. Effects include die and package cracks, fractured wire bonds, package and leadframe delamination, and corrosion of die metallization.

Stress Conditions:

1 Initial Electrical Test Room temperature 2 External Visual Inspection 40X Magnification

3 Temperature Cycling 5 cycles at –40°C (max) to +60°C (min) (Step is optional)

5 Moisture Soak Per MSL rating

6 Preheat Room temp to 140°C in minimum of 80 seconds 6 Solder Immersion 1 full immersion, 10 seconds minimum 7 Flux Application 10 sec immersion in water soluble flux @ room

temp

8 Cleaning Multiple DI water rinses

9 Dry Room temperature

10 Final Electrical Test Room temperature

20. Intermetallic Compound Analysis (IMC) – The use of various solder alloys requires careful analysis to understand the alloy phase compounds present. This is needed to understand what phases are present as each alloy phase will have different physical characteristics.

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The SEM / EDX images shown below show an EDX linescan used to show the elemental composition change across the interface of the solder material and the underlying fab top metallization. This type of analysis is recommended anytime two dissimilar metals are in direct contact and subjected to post processing elevated temperatures (above 100C).

Top down EDX analysis is also recommended to verify the compositional analysis of the solder alloy once deposited on the device surface.

NOTE:*Compositional values translations were done with reference to Cliff-Loremer equation and Ni-Sn phase diagram.

The EDX line scan values were translated to % atom using the Cliff-Loremer equation and Ni-Sn phase diagram to determine the type of IMC present in between the solder and the top metallization (ENiAu).

Remarks:

Ni3Sn4 + Sn and Ni3Sn4 + Ni3Sn2 IMCs were found in between the solder and ENiAu top metallization. These IMC were known to be brittle. 1, 2, 3

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S.W Chen et al. Journal of Electronic Materials Vol. 22 Nov. 11, 2003 2

P.L Tu. IEEE Transactions Components, Packaging, and Manufacturing Technology—Part B, Vol. 20 Issue #1 Feb 1997

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