Esd Protection While Handling Leds: Application Note
Esd Protection While Handling Leds: Application Note
com
Application Note
                                               Valid for:
                                               all OSRAM Opto Semiconductors LEDs
Abstract
This application note gives a first idea of the extensive ESD
protection topic. Because of the enormous scope and the
complexity of the topic only some aspects could be essentially
described and illustrated.
The application note provides information on where to get
further and more detailed information on ESD protection. It is
recommended to consult and use the appropriate standards,
as well as the literature and the publications of the approved
associations and committees.
Table of contents
A. Fundamentals of ESD .............................................................................................3
       Discharge to the device ......................................................................................4
       Discharge from the device ..................................................................................6
B. OSRAM Opto Semiconductors products & their ESD sensitivity ...........................6
C. Considerations of circuit design .............................................................................7
       Breakdown voltage .............................................................................................8
       Response time ....................................................................................................8
       Placement ...........................................................................................................8
D. Typical symptoms of ESD damage ........................................................................9
       Possible causes ................................................................................................10
       Analytical techniques ........................................................................................10
E. Where to take care of ESD? ..................................................................................10
F. Recommendations for ESD control .......................................................................10
       Grounding / bonding systems ..........................................................................10
       Personal grounding ...........................................................................................10
       Protected areas ................................................................................................11
       Packaging .........................................................................................................11
       Marking .............................................................................................................11
       Equipment .........................................................................................................12
       Handling ............................................................................................................12
G. ESD control checklist ...........................................................................................14
       Grounding / general ESD controls ....................................................................14
       Storage / stationing/ transfer of materials ........................................................16
       Plant ESD control program ...............................................................................17
       ESD control training / certification ....................................................................17
H. Monitoring an ESD control program .....................................................................17
I. References .............................................................................................................19
A. Fundamentals of ESD
           As LED’s become more efficient and more compact their sensitivity to ESD
           events is also increasing in the majority of cases. Despite a great deal of effort in
           the semiconductor industry in the past decade, ESD still affects production
           yields, manufacturing costs, product quality, product reliability, and profitability
           of all semiconductor devices, including LED’s. The cost of the damaged device
           itself is often negligible, but if associated costs like repair and rework, shipping,
           labour and overhead are included, clearly there is a need to understand how to
           handle and process devices which are sensitive to ESD.
           Controlling electrostatic discharge begins with understanding how electrostatic
           charge occurs in the first place. Electrostatic charge is most commonly created
           by the contact and separation of two materials, which is known as “tribo-electric
           charging” (see Figure 1).
           It involves the transfer of electrons between materials. When two materials are
           placed in contact and then separated, negatively charged electrons are
           transferred from the surface of one material to the surface of the other material.
           Which material loses electrons and which gains electrons will depend on the
           nature of the two materials. The material that loses electrons becomes positively
           charged, while the material that gains electrons is negatively charged.
           For example, a person walking across the floor generates static electricity as
           shoe soles contact and then separate from the floor surface. An electronic device
           sliding into or out of a bag, magazine or tube generates an electrostatic charge
           as the device's housing and metal leads make multiple contacts and separations
           with the surface of the container. While the magnitude of electrostatic charge
           may be different in these examples, static electricity is indeed generated.
           discharged through a switching component (S1) and a 1.5 kΩ series resistor (R1)
           into the component. A typical Human Body Model circuit, as described in ANSI/
           ESDA/JEDEC JS-001-2017, is shown in Figure 2.
S1 R1
                                                             1500 Ω
                                                                             Terminal A
High voltage
                                                                                           500 Ω
                                                                                   Short
              pulse                      C1       100 pF            S2    DUT                      R2
              generator                                                   Sockel
Terminal B
           MM model. A discharge similar to the HBM event also can occur from a charged
           conductive object, such as a metallic tool or fixture. Originating in Japan as the
           result of trying to create a worst-case HBM event, the model is known as the
           Machine Model (MM). This ESD model consists of a 200 pF capacitor discharged
           directly into a component with no series resistor (Figure 3).
0.5 μH
           As a worst-case human body model, the Machine Model may be over severe.
           However, there are real situations that this model represents, for example the
           rapid discharge from a charged board assembly or from the charged cables of
           an automatic tester. The MM version does not have a 1.5 kΩ resistor, but
           otherwise the test board and the socket are the same as for HBM testing. The
           series inductance, as shown in Figure 3, is the dominating parasitic element that
           shapes the oscillating machine model wave form.
           Figure 5: Micro SIDELED® 3030 with ThinGaN chip and no ESD protection diode, due
           to space restrictions (ANSI/ESDA/JEDEC JS-001 (HBM, Class 0))
           Breakdown voltage
           When a surge occurs (see Figure 7) and exceeds the maximum ratings of the
           LED, the Zener diode provides an alternative path to channelize the current.
           Figure 7: The most commonly used waveform of ESD discharge defined by IEC 61000-
           4-2 [4]
                   Ipeak
               100%
                   90%
at 30 ns
at 60 ns
10%
                             30
                                     60
                                      Time [ns]
           Response time
           The response time of dedicated protection diode has to be faster than the LEDs.
           Thus the mechanism can work effectively before a pulse might cause any
           damage to the LEDs. Due to the short switching time of LEDs, the response time
           of protection device is supposed to be in the range of nanoseconds or less. Note
           that this characteristic has to be considered in both directions from anode to
           cathode, and vice versa.
           Placement
           An ESD protection device ought to be placed near by the power input in order to
           protect the whole module from incoming surges of power supply. However, to
           prevent damage which occurs from other sources, for instance by touching the
           PCB, the most applicable location should be placed the closest to the protected
           circuitry, i.e. LEDs. An appropriate way to locate the component therefore would
           vary from one case to another. Designer must first identify where the most
           potential damage could come from.
           The above-mentioned precautions should be pre-examined before any designer
           going about selecting the appropriate protective devices.
           Figure 8: Typical failure of ESD impairment (3 kV, analysis with FIB and SEM)
                                                                     Melted hole visible with SEM
                                                                     after further preparation
Au bondpad
Semiconductor
Figure 9: Typical failure of EOS deterioration (analysis with FIB and SEM)
Melted nitride
Bondpad
Semiconductor
           Possible causes
           Static discharge is almost always associated with people, the type of material/
           clothes that people wear and/or the handling equipment.
           Analytical techniques
           1.      Electrical characterization — Curve tracer
           2.      Optical detection — Optical microscopy
           3.      Physical identification — Scanning electron microscope
           Personal grounding
           All personnel shall be bonded or electrically connected to the ground or
           contrived ground when handling ESD sensitive items. When personnel are
           seated at ESD protective workstations, they shall be connected to the common
           point ground via a wrist strap system.
           Protected areas
           Handling of ESDS parts, assemblies and equipment without ESD protective
           covering or packaging shall be performed in a protected area (Figure 10).
           Caution signs indicating the existence of the protected area shall be posted and
           clearly visible to personnel prior to entry to the protected area. ESDS items shall
           be packaged in ESD protective packaging while not in a protected area. Access
           to the protected area shall be limited to personnel who have completed
           appropriate ESD training. Trained personnel shall escort untrained individuals
           while in a protected area. All nonessential insulators, such as those made of
           plastics and paper (e.g. coffee cups, food wrappers and personal items) must be
           removed from the workstation. Ionization or other charge mitigating techniques
           shall be used at the workstation to neutralize electrostatic fields on all process
           essential insulators (e.g. ESDS device parts, device carriers and specialized
           tools) if the electrostatic field is considered a threat.
           Packaging
           ESD protective packaging and package marking shall be in accordance with the
           recommendation of the standards. For smooth business processes ESD
           protective packaging can be defined and fixed in the contract, purchase order,
           drawing or other documentation. Packaging shall be defined for all material
           movement within protected areas, between job sites and field service
           operations.
           Marking
           ESDS assemblies and equipment containing ESDS parts and assemblies should
           be marked with an ESD caution symbol, (i.e., EOS/ESD S8.1). The symbol should
           also be located on equipment in a position readily visible to personnel. In
           addition, the symbol should be located in a position readily visible when an ESDS
           assembly is incorporated into its next higher assembly.
           Equipment
           •       AC powered tools
                   The working part of AC powered tools should be capable of providing a
                   conductive path to ground. New powered hand tools such as soldering
                   irons typically should have a tip to ground resistance of less than 1.0 Ω.
                   Note — This resistance may increase with use but should be less than
                   20.0 Ω for verification purposes.
           •       Battery powered and pneumatic hand tools
                   Battery powered and pneumatic hand tools while being held should have a
                   resistance to ground of less than 1 x 1012 Ω.
           •       Automated handlers
                   All conductive or static dissipative components of automated handling
                   equipment should provide a continuous conductive path to ground,
                   whether stationary or in motion. The equipment should minimize charge
                   generation of the ESDS items that are handled. Where insulating materials
                   are necessary in the device path, they should be designed to minimize
                   electric fields and the charge imparted to devices being handled.
           Handling
           ESD protective handling procedures shall be established, documented, and
           implemented. Handling procedures are required for all areas where ESDS items
           are manually or machine processed. When outside their protective covering or
           packaging, ESDS items shall be handled only in a protected area.
                                 Receiving
                                              Stores &               Automatic        Manual
                                 & incoming              Kitting
                                              storage                insertion        Inspection
                                 inspection
            Wrist bands               •          •           •                            •
            Worksurface mats         •                       •                            •
            Floor mats                •          •           •             •              •
            Shoe grounders           •           •           •                            •
            Clothing                  •          •           •                            •
            Shielding bags            •          •           •                            •
            Conductive foam                      •           •                            •
            Conductive                •          •           •                            •
            containers
            Field service kit/
            mat
            Ionizers                 •                       •             •              •
                                              Board
                                 Wave                    Equipment       Packaging      Field
                                              testing
                                 soldering               assembly        & shipping     service
                                              rework
            Wrist bands                          •            •                •              •
            Worksurface mats                     •            •                •              •
            Floor mats                •          •            •                •
            Shoe grounders            •          •            •                •
            Clothing                             •            •
            Shielding bags                       •            •                •              •
            Conductive foam                      •                             •              •
            Conductive con-           •          •            •                               •
            tainers
            Field service kit/                                                                •
            mat
            Ionizers                  •          •                                            •
                   areas?
           16. Are ESD protective garments correctly worn?
                     (M6) Measure the resistivity of the ESD protective garment/smock; Spec:
                          0 — 1E5 Ω/Square
           17. Are the ground points of all equipment grounded to the common ESD
               ground of the plant?
                     (M7) Measure the resistances between equipment ESD ground points
                         and the common ESD ground; Spec: < 1 Ω
                     (M8) Measure field voltages around the equipment; Spec: < 200 V
           18. Are non-grounded personnel at least 4 feet away from any ESD sensitive
               area?
           19. Are charge-generating equipment at least 4 feet away from any ESD
               sensitive area?
           20. Is the surface of the worktable where ESD-sensitive devices are handled
               covered with a static dissipative mat?
           21. Is the static dissipative mat on the table properly grounded to the ESD
               common ground at prescribed intervals?
                     (M9) Measure the resistivity of the worktable surface;
                          Spec: 1 E5 — 1E9 Ω/Square
                     (M10) Measure the resistance of the dissipative mat ground point to the
                         common ESD ground; Spec: < 1 Ω
                     (M11) Measure field voltages at different areas of the worktable surface;
                         Spec: < 200 V
           22. Are the ground points of workstations and equipment properly labeled as
               such?
           23. Does the plant have a prescribed procedure and frequency for cleaning
               their ESD protective flooring/surfaces to maintain their conductive /
               dissipative properties?
           24. Are there any non-essential personal items in the ESD controlled areas?
                     (M12) Measure field voltages around any non-essential personal items;
                         Spec: < 200 V
           25. Are there any insulating materials in ESD controlled areas, e.g., plastic
               bags, plastic envelopes, plastic folders, boxes?
           26. Where insulating materials are present in ESD controlled areas, are ionizers
               in use?
           27. Where ionizers are in use, are these ionizers properly positioned and
           Table 3 gives recommendation for the time intervals for ESD monitoring.
           Table shows the ESD classification criteria according to ANSI/ESDA/JEDEC JS-
           001 (HBM). Table 5 depicts the ESD classification criteria according to ANSI/
           ESDA/JEDEC JS-002 (CDM).
            Classification
                                Classification test condition
            level
            Class 0             Any part that fails after exposure to an ESD pulse of 250 V or less.
            Class 1A            Any part that passes after exposure ton an ESD pulse of 250 V, but
                                fails after exposure to an ESD pulse of 500 V.
            Class 1B            Any part that passes after exposure to an ESD pulse of 500 V, but
                                fails after exposure to an ESD pulse of 1,000 V.
            Class 1C            Any part that passes after exposure to an ESD pulse of 1,000 V, but
                                fails after exposure to an ESD pulse of 2,000 V.
            Class 2             Any part that passes after exposure to an ESD pulse of 2,000 V, but
                                fails after exposure to an ESD pulse of 4,000 V.
            Class 3A            Any part that passes after exposure to an ESD pulse of 4,000 V, but
                                fails after exposure to an ESD pulse of 8,000 V.
            Class 3B            Any part that passes after exposure to an ESD pulse of 8,000 V.
            Classification
                              Classification test condition
            level
            Class 0a          Any part that fails after exposure to an ESD pulse of 125 V or less.
            Class 0b          Any part that passes after exposure ton an ESD pulse of 125 V, but
                              fails after exposure to an ESD pulse of 250 V.
            Class 1           Any part that passes after exposure ton an ESD pulse of 250 V, but
                              fails after exposure to an ESD pulse of 500 V.
            Class 2a          Any part that passes after exposure ton an ESD pulse of 500 V, but
                              fails after exposure to an ESD pulse of 750 V.
            Class 2b          Any part that passes after exposure ton an ESD pulse of 750 V, but
                              fails after exposure to an ESD pulse of 1,000 V.
            Class 3           Any part that passes after exposure to an ESD pulse of 1,000 V.
I. References
           [1]     JEDEC Solid State Technology Association, https://www.jedec.org/.
           [2]     ANSI/ESDA/JEDEC       JS-001-2017,      Human      Body    Model     (HBM)    —
                   Component Level.
           [3]     JEDEC JEP 172A, Discontinuing Use of the Machine Model for Device ESD
                   Qualification, 2015.
           [4]     ANSI/ESDA/JEDEC JS-002-2014, Charged Device Model (CDM) — Device
                   Level.
           [5]     IEC 61000-4-2:2008, Electromagnetic compatibility (EMC) Part 4-2: Testing
                   and measurement techniques — Electrostatic discharge immunity test.
           [6]     IEC 61340-5-1:2016, Electrostatics — Part 5-1: Protection of electronic
                   devices from electrostatic phenomena — General requirements.
           [7]     ANSI/ESD S20.20-2014, Protection of Electrical and Electronic Parts,
                   Assemblies and Equipment (Excluding Electrically Initiated Explosive
                   Devices).
           [8]     Stephen A. Halperin, Guidelines for Static Control Management, Eurostat,
                   1990.
           [9]     ESD TR 20.20:2008, ESD Handbook, Electrostatic Discharge Association,
www.ledlightforyou.com
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