Concentrator photovoltaic (CPV) solar cells and cell on carrier (CoC) assemblies - Qualification

IEC 62787:2021 specifies the minimum requirements for the qualification of concentrator photovoltaic (CPV) cells and Cell on Carrier (CoC) assemblies for incorporation into CPV receivers, modules and systems. The object of this qualification standard is to determine the optoelectronic, mechanical, thermal, and processing characteristics of CPV cells and CoCs to show that they are capable of withstanding assembly processes and CPV application environments. The qualification tests of this document are designed to demonstrate that cells or CoCs are suitable for typical assembly processes, and when properly assembled, are capable of passing IEC 62108.
This document defines qualification testing for two levels of concentrator photovoltaic device assembly:
a) cell, or bare cell; and
b) cell on carrier (CoC).

Cellules solaires photovoltaïques à concentration (PVC) et ensembles de cellules sur support (CoC) - Qualification

IEC 62787:2021 spécifie les exigences minimales relatives à la qualification des cellules photovoltaïques à concentration (CPV) et des assemblages de cellules sur support (CoC) pour intégration dans les récepteurs, modules et systèmes CPV.
La présente norme de qualification a pour objet de déterminer les caractéristiques optoélectroniques, mécaniques, thermiques et de traitement des cellules CPV et des CoC afin de montrer qu’elles sont capables de résister aux processus de l’assemblage et aux environnements d’application des CPV. Les essais de qualification du présent document visent à démontrer que les cellules ou les CoC sont adaptées à des processus d’assemblage classiques, et qu’elles sont capables de satisfaire à l’IEC 62108 si elles sont correctement assemblées.
Le présent document définit les essais de qualification pour deux niveaux d’un ensemble de dispositifs photovoltaïques à concentration:
a) cellule (ou cellule nue), et
b) cellule sur support (CoC).

General Information

Status
Published
Publication Date
02-Feb-2021
Current Stage
PPUB - Publication issued
Completion Date
03-Feb-2021
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IEC 62787
Edition 1.0 2021-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside

Concentrator photovoltaic (CPV) solar cells and cell on carrier (CoC) assemblies –

qualification
Cellules solaires photovoltaïques à concentration (PVC) et ensembles de
cellules sur support (CoC) – Qualification
IEC 62787:2021-02(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 62787
Edition 1.0 2021-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside

Concentrator photovoltaic (CPV) solar cells and cell on carrier (CoC) assemblies –

qualification
Cellules solaires photovoltaïques à concentration (PVC) et ensembles de
cellules sur support (CoC) – Qualification
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.160 ISBN 978-2-8322-9326-3

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---------------------- Page: 3 ----------------------
– 2 – IEC 62787:2021 © IEC 2021
CONTENTS

FOREWORD ........................................................................................................................... 4

1 Scope .............................................................................................................................. 6

2 Normative references ...................................................................................................... 6

3 Terms and definitions ...................................................................................................... 7

4 Operating environment .................................................................................................... 9

5 Sampling ......................................................................................................................... 9

6 Marking ......................................................................................................................... 10

7 Characterization methods for measuring the performance of bare cells and CoCs

subjected to qualification tests ....................................................................................... 10

7.1 General ................................................................................................................. 10

7.2 Light I-V measurement .......................................................................................... 10

7.3 Dark I-V measurement .......................................................................................... 11

7.3.1 General ......................................................................................................... 11

7.3.2 Procedure ...................................................................................................... 11

7.4 Electroluminescence (EL) mapping ....................................................................... 11

7.5 X-ray and Scanning Acoustic Microscope (SAM) ................................................... 12

7.6 Visual inspection ................................................................................................... 12

7.7 Thermal resistance measurement ......................................................................... 12

8 Pass criteria .................................................................................................................. 13

9 Documentation and reporting ......................................................................................... 20

10 Modifications and requalification .................................................................................... 20

11 Qualification stress tests ............................................................................................... 21

11.1 General ................................................................................................................. 21

11.2 ESD damage threshold ......................................................................................... 21

11.2.1 General ......................................................................................................... 21

11.2.2 Purpose ......................................................................................................... 21

11.2.3 Procedure ...................................................................................................... 22

11.2.4 Requirements ................................................................................................ 22

11.3 Front and back metal adhesion ............................................................................. 22

11.3.1 Purpose ......................................................................................................... 22

11.3.2 Procedure ...................................................................................................... 22

11.3.3 Requirements ................................................................................................ 22

11.4 High-temperature storage ..................................................................................... 22

11.4.1 Purpose ......................................................................................................... 22

11.4.2 Procedure ...................................................................................................... 22

11.4.3 Requirements ................................................................................................ 23

11.5 Thermal cycling..................................................................................................... 23

11.5.1 Purpose ......................................................................................................... 23

11.5.2 Procedure ...................................................................................................... 23

11.5.3 Requirements ................................................................................................ 24

11.6 High temperature with current injection ................................................................. 24

11.6.1 Purpose ......................................................................................................... 24

11.6.2 Procedure ...................................................................................................... 25

11.6.3 Requirements ................................................................................................ 25

11.7 Low level light biased damp heat .......................................................................... 25

11.7.1 Purpose ......................................................................................................... 25

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IEC 62787:2021 © IEC 2021 – 3 –

11.7.2 Procedure ...................................................................................................... 25

11.7.3 Requirements ................................................................................................ 25

11.8 Solderability .......................................................................................................... 26

11.8.1 Purpose ......................................................................................................... 26

11.8.2 Procedure ...................................................................................................... 26

11.8.3 Requirements ................................................................................................ 27

11.9 Illumination ........................................................................................................... 27

11.9.1 Purpose ......................................................................................................... 27

11.9.2 Procedure ...................................................................................................... 27

11.9.3 Requirements ................................................................................................ 28

11.10 Wire/Ribbon bond strength .................................................................................... 28

11.10.1 Purpose ......................................................................................................... 28

11.10.2 Procedure ...................................................................................................... 28

11.10.3 Requirements ................................................................................................ 30

11.11 Die adhesion ......................................................................................................... 31

11.11.1 Purpose ......................................................................................................... 31

11.11.2 Procedure ...................................................................................................... 31

11.11.3 Requirements ................................................................................................ 31

11.12 Connector shear strength ...................................................................................... 32

11.12.1 Purpose ......................................................................................................... 32

11.12.2 Procedure ...................................................................................................... 32

11.12.3 Pass/fail criteria ............................................................................................. 33

11.13 Bypass diode shear strength ................................................................................. 33

11.13.1 Purpose ......................................................................................................... 33

11.13.2 Procedure ...................................................................................................... 33

11.13.3 Requirements ................................................................................................ 33

Figure 1 – Schematics and photos of Cells on Carrier and bare cell test assembly ................. 8

Figure 2 – Representative samples of CPV systems, where cells and CoCs are

deployed ................................................................................................................................. 9

Figure 3 – Flow chart of qualification tests for bare solar cells .............................................. 18

Figure 4 – Flow chart of qualification tests for CoCs ............................................................. 19

Figure 5 – Thermal Cycle Diagram for the CoC test and TCO-1 ............................................ 24

Figure 6 – Force diagram in the bond strength test (taken from IEC 60749-22:2002,

Annex A, Method B) .............................................................................................................. 29

Figure 7 – Minimum bond pull limits (normal to die) (taken from IEC 60749-22:2002,

Annex A, Method B) .............................................................................................................. 30

Figure 8 – Schematic of the test set up for the die adhesion test........................................... 31

Figure 9 – Die shear strength criteria (minimum force versus die attach area) (taken

from MIL.ST-883-K) .............................................................................................................. 32

Figure 10 – Schematics of the position of the pushing tool (taken from

IEC 62137-1-2:2007) ............................................................................................................ 33

Table 1 – Qualification tests description for bare solar cells .................................................. 14

Table 2 – Qualification tests description for CoCs ................................................................. 16

Table 3 – Thermal Cycle Options (TCO) of test 11.5 for CoCs .............................................. 23

Table 4 – Minimum pulling forces, PW (taken from IEC60749-22:2002, Method B) ................ 29

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– 4 – IEC 62787:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
CONCENTRATOR PHOTOVOLTAIC (CPV) SOLAR CELLS
AND CELL ON CARRIER (CoC) ASSEMBLIES –
QUALIFICATION
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international

co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and

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Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.

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Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

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any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.

5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

services carried out by independent certification bodies.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent

rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 62787 has been prepared by subcommittee 82: Solar photovoltaic

energy systems.
The text of this International Standard is based on the following documents:
FDIS Report on voting
82/1818/FDIS 82/1834/RVD

Full information on the voting for the approval of this International Standard can be found in the

report on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

---------------------- Page: 6 ----------------------
IEC 62787:2021 © IEC 2021 – 5 –

The committee has decided that the contents of this document will remain unchanged until the

stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to

the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

IMPORTANT – The "colour inside" logo on the cover page of this document indicates

that it contains colours which are considered to be useful for the correct understanding

of its contents. Users should therefore print this document using a colour printer.

---------------------- Page: 7 ----------------------
– 6 – IEC 62787:2021 © IEC 2021
CONCENTRATOR PHOTOVOLTAIC (CPV) SOLAR CELLS
AND CELL ON CARRIER (CoC) ASSEMBLIES –
QUALIFICATION
1 Scope

This document specifies the minimum requirements for the qualification of concentrator

photovoltaic (CPV) cells and Cell on Carrier (CoC) assemblies for incorporation into CPV

receivers, modules and systems.

The object of this qualification standard is to determine the optoelectronic, mechanical, thermal,

and processing characteristics of CPV cells and CoCs to show that they are capable of

withstanding assembly processes and CPV application environments. The qualification tests of

this document are designed to demonstrate that cells or CoCs are suitable for typical assembly

processes, and when properly assembled, are capable of passing IEC 62108.

This document defines qualification testing for two levels of concentrator photovoltaic device

assembly:
a) cell, or bare cell; and
b) cell on carrier (CoC).

NOTE Note that a variety of alternate names are used within the industry, such as solar cell assembly, receiver,

etc.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies.

For undated references, the latest edition of the referenced document (including any

amendments) applies.

IEC 60721-2-1:2013, Classification of environmental conditions – Part 2-1: Environmental

conditions appearing in nature – Temperature and humidity

IEC 60749-3:2017, Semiconductor devices – Mechanical and climatic test methods – Part 3:

External visual examination

IEC 60749-6:2017, Semiconductor devices – Mechanical and climatic test methods – Part 6:

Storage at high temperature

IEC 60749-14:2003, Semiconductor devices – Mechanical and climatic test methods – Part 14:

Robustness of terminations (lead integrity)

IEC 60749-21:2011, Semiconductor devices – Mechanical and climatic test methods – Part 21:

Solderability

IEC 60749-22:2002, Semiconductor devices – Mechanical and climatic test methods – Part 22:

Bond strength

IEC 60904-1-1:2017, Photovoltaic devices – Part 1-1: Measurement of current-voltage

characteristics of multi-junction photovoltaic (PV) devices
---------------------- Page: 8 ----------------------
IEC 62787:2021 © IEC 2021 – 7 –
IEC 61000-4-2:2008, Electromagnetic compatibility (EMC) – Part 4-2: Testing and
measurement techniques – Electrostatic discharge immunity test

IEC 61193-2:2007, Quality assessment systems – Part 2 selection and use of sampling plans

for inspection of electronic components and packages

IEC TS 61836:2016, Solar photovoltaic energy systems – Terms, definitions and symbols

IEC 62108:2016, Concentrator photovoltaic (CPV) modules and assemblies – Design
qualification and type approval

IEC 62137-1-2:2007, Surface mounting technology – Environmental and endurance test

methods for surface mount solder joint – Part 1-2: Shear strength test

IEC 62670-1:2013, Photovoltaic concentrators (CPV) – Performance testing – Part 1: Standard

conditions
IEC TS 62789:2014, Photovoltaic concentrator cell documentation

IEC 63202-2, Photovoltaic cells – Part 2: Electroluminescence image for crystalline silicon

solar cells

ECSS-E-ST-20-08C Rev 1, 18 July 2012, Space engineering – Photovoltaic assemblies and

components – Part 7.5.8: Coating adherence (CA)

MIL.ST-883-K, Test Method Standard – Microcircuits Method 2019.9 Die shear strength

3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC TS 61836 and

IEC 62108 apply, as well as the following.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
bare cell

refers to a semiconductor die level. The physical form during a commercial transaction may be

a separated solar cell, a diced wafer on tape, or even a processed wafer. The one common

denominator is that the qualified configuration is completely unprotected and not ready for

interconnection with the rest of a CPV module

Note 1 to entry: For this qualified configuration, the customer is responsible for all integration and assembly.

Note 2 to entry: For some qualification tests, bare cells are mounted on a substrate, heatsink, or other type of

carrier (see Figure 1c). This provides mechanical stability, robust electrical contacts, and appropriate thermal

management, but it is not considered in the bare solar cell qualification.
3.2
Cell on Carrier
CoC

cell bonded and interconnected with a cell carrier, at a minimum (see Figure 1b). This is a

relatively small, assembled unit in a relatively complete and rugged package
---------------------- Page: 9 ----------------------
– 8 – IEC 62787:2021 © IEC 2021

Note 1 to entry: A cell on carrier can optionally include a bypass diode, encapsulation of the cell and/or

interconnects and a connector to simplify series or parallel connection. Alternatively, a CoC can also include multiple

cells. A CoC does not include any optical element.

Note 2 to entry: Figure 1 shows an expanded schematic of common components in a CoC, along with two photos.

Note that these photos illustrate relatively simple packages containing one primary photovoltaic device.

a) CoC exploded schematic

b) Cell on Carrier (CoC) with connectors and 2x c) Bare cell test assembly is intended to provide a

packaged diodes. Intended for sale in this test vehicle for bare cell qualification. Bypass diodes

configuration. can be included or not. Not a CoC offered for sale.
Figure 1 – Schematics and photos of Cells on Carrier and bare cell test assembly
---------------------- Page: 10 ----------------------
IEC 62787:2021 © IEC 2021 – 9 –
3.3
supplier

any entity that supplies CPV wafers (diced or undiced), CPV solar cells (separated on foils in

sawing frames, single cells in trays or in reel) or CoCs to a customer
3.4
customer
any entity that buys some of these products from the supplier
4 Operating environment

CPV systems are typically designed to be operated in the “open-air climates" defined in

IEC 60721-2-1 except the Polar one. Depending on the details of the system design, the bare

solar cells and CoCs may or may not be protected from exposure to damp heat, freezing,

condensation, and other elements of the CPV application environment. Figure 2 shows

schematics of two CPV system designs.

Figure 2 – Representative samples of CPV systems, where cells and CoCs are deployed

Regardless of the specific design approach taken, the high incident irradiance impinging on the

solar cells in CPV systems will cause them to operate at (local) temperatures that can be

significantly higher than the maximum ambient temperature specified for the system as a whole.

5 Sampling

Device samples used in qualification testing shall be selected randomly in accordance with

IEC 61193-2 from a minimum of two manufacturing batches and subjected to the defined

Process Identification Document (PID) manufacturing and screening steps.
---------------------- Page: 11 ----------------------
– 10 – IEC 62787:2021 © IEC 2021

The number of devices to be tested in each qualification test shall not be less than the sample

sizes specified in Clause 8. In order to provide statistical meaning to the number of devices,

IEC 61193-2 has been used since it assigns a defect probability as a function of number of

samples.

The samples for each test of Table 1 and Table 2 shall be chosen randomly from the

000 bare cells/CoCs.
qualification lot. The qualification lot shall be a production lot of at least 1

The production lot shall be formed from at least two epitaxial runs and three metal/ARC

depositions carried out in different weeks.
6 Marking

Due to the very small bare solar cell dimensions any marking on cell is usually not possible.

The
...

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