IEC 60749-20:2008

IEC 60749-20
Edition 2.0 2008-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Semiconductor devices – Mechanical and climatic test methods –
Part 20: Resistance of plastic encapsulated SMDs to the combined effect of
moisture and soldering heat
Dispositifs à semiconducteurs – Méthodes d'essais mécaniques et climatiques –
Partie 20: Résistance des CMS à boîtier plastique à l'effet combiné de l'humidité
et de la chaleur de brasage
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IEC 60749-20
Edition 2.0 2008-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Semiconductor devices – Mechanical and climatic test methods –
Part 20: Resistance of plastic encapsulated SMDs to the combined effect of
moisture and soldering heat
Dispositifs à semiconducteurs – Méthodes d'essais mécaniques et climatiques –
Partie 20: Résistance des CMS à boîtier plastique à l'effet combiné de l'humidité
et de la chaleur de brasage
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
U
CODE PRIX
ICS 31.080.01 ISBN 978-2-88910-284-6
– 2 – 60749-20 © IEC:2008
CONTENTS
FOREWORD.4
1 Scope.6
2 Normative references.6
3 General description.6
4 Test apparatus and materials.6
4.1 Humidity chamber.6
4.2 Reflow soldering apparatus.6
4.3 Holder .7
4.4 Wave-soldering apparatus .7
4.5 Solvent for vapour-phase reflow soldering.7
4.6 Flux.7
4.7 Solder .7
5 Procedure.7
5.1 Initial measurements .7
5.1.1 Visual inspection.7
5.1.2 Electrical measurement.8
5.1.3 Internal inspection by acoustic tomography .8
5.2 Drying.8
5.3 Moisture soak .8
5.3.1 General .8
5.3.2 Conditions for non-dry-packed SMDs .8
5.3.3 Moisture soak for dry-packed SMDs .8
5.4 Soldering heat .10
5.4.1 General .10
5.4.2 Method of heating by infrared convection or convection reflow
soldering.11
5.4.3 Method of heating by vapour-phase reflow soldering.12
5.4.4 Method of heating by wave-soldering.12
5.5 Recovery .13
5.6 Final measurements .14
5.6.1 Visual inspection.14
5.6.2 Electrical measurement.14
5.6.3 Internal inspection by acoustic tomography .14
6 Information to be given in the relevant specification.14
Annex A (informative) Details and descriptions of test method on resistance of plastic
encapsulated SMDs to the combined effect of moisture and soldering heat.16

Figure 1 – Method of measuring the temperature profile of a specimen.7
Figure 2 – Heating by wave-soldering .13
Figure A.1 – Process of moisture diffusion at 85 °C, 85 % RH.17
Figure A.2 – Definition of resin thickness and the first interface .17
Figure A.3 – Moisture soak time to saturation at 85 °C as a function of resin thickness .18
Figure A.4 – Temperature dependence of saturated moisture content of resin.18
Figure A.5 – Dependence of moisture content of resin at the first interface on resin
thickness under various soak conditions.19

60749-20 © IEC:2008 – 3 –
Figure A.6 – Dependence of moisture content of resin at the first interface on resin
thickness related to method A of moisture soak .20
Figure A.7 – Dependence of the moisture content of resin at the first interface on resin
thickness related to method B of moisture soak .21
Figure A.8 – Dependence of moisture content of resin at the first interface on resin
thickness related to condition B2 of method B of moisture soak .21
Figure A.9 – Temperature profile of infrared convection and convection reflow soldering
for Sn-Pb eutectic assembly.23
Figure A.10 – Temperature profile of infrared convection and convection reflow
soldering for lead-free assembly.23
Figure A.11 – Classification profile .25
Figure A.12 – Temperature profile of vapour-phase soldering (condition II-A).25
Figure A.13 – Immersion method into solder bath .26
Figure A.14 – Relation between the infrared convection reflow soldering and wave-
soldering.26
Figure A.15 – Temperature in the body of the SMD during wave-soldering .27

Table 1 – Moisture soak conditions for non-dry-packed SMDs .8
Table 2 – Moisture soak conditions for dry-packed SMDs (method A) .9
Table 3 – Moisture soak conditions for dry-packed SMDs (method B) .10
Table 4 – SnPb eutectic process – Classification reflow temperatures .11
Table 5 – Pb-free process – Classification reflow temperatures .12
Table 6 – Heating condition for vapour-phase soldering .12
Table 7 – Immersion conditions for wave-soldering.13
Table A.1 – Comparison of actual storage conditions and equivalent moisture soak

conditions before soldering heat.18
Table A.2 – Classification profiles.24

– 4 – 60749-20 © IEC:2008
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SEMICONDUCTOR DEVICES –
MECHANICAL AND CLIMATIC TEST METHODS –

Part 20: Resistance of plastic encapsulated SMDs to
the combined effect of moisture and soldering heat

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
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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
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
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
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Publications.
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 60749-20 has been prepared by IEC technical committee 47:
Semiconductor devices.
This second edition cancels and replaces the first edition published in 2002 and constitutes a
technical revision. The main changes are as follows:
• to reconcile certain classifications of IEC 60749-20 and those of IPC/JEDEC J-STD-020C;
• reference IEC 60749-35 instead of Annex A of IEC 60749-20, Edition 1;
• update for lead-free solder;
• correct certain errors in the original Edition 1.

60749-20 © IEC:2008 – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
47/1989/FDIS 47/2003/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the IEC 60749 series, under the general title Semiconductor devices –
Mechanical and climatic test methods, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until the
maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – 60749-20 © IEC:2008
SEMICONDUCTOR DEVICES –
MECHANICAL AND CLIMATIC TEST METHODS –

Part 20: Resistance of plastic encapsulated SMDs to
the combined effect of moisture and soldering heat

1 Scope
This part of IEC 60749 provides a means of assessing the resistance to soldering heat of
semiconductors packaged as plastic encapsulated surface mount devices (SMDs). This test is
destructive.
2 Normative references
The following referenced documents are indispensable for the application 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 60068-2-20:2008, Environmental testing – Part 2-20: Tests – Test T: Test methods for
solderability and resistance to soldering heat of devices with leads
IEC 60749-3, Semiconductor devices – Mechanical and climatic test methods – Part 3: External
visual inspection
IEC 60749-35, Semiconductor devices – Mechanical and climatic test methods – Part 35:
Acoustic microscopy for plastic encapsulated electronic components
3 General description
Package cracking and electrical failure in plastic encapsulated SMDs can result when soldering
heat raises the vapour pressure of moisture which has been absorbed into SMDs during
storage. These problems are assessed. In this test method, SMDs are evaluated for heat
resistance after being soaked in an environment which simulates moisture being absorbed
while under storage in a warehouse or dry pack.
4 Test apparatus and materials
4.1 Humidity chamber
The humidity chamber shall provide an environment complying with the temperature and
relative humidity defined in 5.3.
4.2 Reflow soldering apparatus
The infrared convection, the convection and the vapour-phase reflow soldering apparatus shall
provide temperature profiles complying with the conditions of soldering heat defined in 5.4.2
and 5.4.3. The settings of the reflow soldering apparatus shall be adjusted by temperature
profiling of the top surface of the specimen while it is undergoing the soldering heat process,
measured as shown in Figure 1.

60749-20 © IEC:2008 – 7 –
Adhesive agent or thin tape
Thermocouple
Die
Lead pins
Resin
Holder
IEC  1746/01
NOTE The adhesive agent or thin tape should have good thermal conductivity.
Figure 1 – Method of measuring the temperature profile of a specimen
4.3 Holder
Unless otherwise detailed in the relevant specification, any board material, such as epoxy
fibreglass or polyimide, may be used for the holder. The specimen shall be placed on the
holder by the usual means and in a position as shown in Figure 1. If the position of the
specimen, as shown in Figure 1, necessitates changing the shape of terminations and results
in subsequent electrical measurement anomalies, a position that avoids changing the shape of
terminations may be chosen, and this shall be specified in the relevant specification.
4.4 Wave-soldering apparatus
The wave-soldering apparatus shall comply with conditions given in 5.4.4. Molten solder shall
usually be flowed.
4.5 Solvent for vapour-phase reflow soldering
Perfluorocarbon (perfluoroisobutylene) shall be used.
4.6 Flux
Unless otherwise detailed in the relevant specification, the flux shall consist of 25 % by weight
of colophony in 75 % by weight of isopropyl alcohol, both as specified in Annex B of IEC 60068-
2-20:2008.
4.7 Solder
Solder of composition as specified in Table 1 of IEC 60068-2-20:2008 shall be used.
5 Procedure
5.1 Initial measurements
5.1.1 Visual inspection
Visual inspection, as specified in IEC 60749-3, shall be performed before the test. Special
attention shall be paid to external cracks and swelling, which will be looked for under a
magnification of 40×.
– 8 – 60749-20 © IEC:2008
5.1.2 Electrical measurement
Electrical testing shall be performed as required by the relevant specification.
5.1.3 Internal inspection by acoustic tomography
Unless otherwise detailed in the relevant specification, internal cracks and delamination in the
specimen shall be inspected by acoustic tomography in accordance with IEC 60749-35.
5.2 Drying
Unless otherwise detailed in the relevant specification, the specimen shall be baked at 125 °C
± 5 °C for at least 24 h.
5.3 Moisture soak
5.3.1 General
Unless otherwise detailed in the relevant specification, moisture soak conditions shall be
selected on the basis of the packing method of the specimen (see A.1.1). If baking the
specimen before soldering is detailed in the relevant specification, the specimen shall be baked
instead of being subject to moisture soak.
5.3.2 Conditions for non-dry-packed SMDs
The moisture soak condition shall be selected from Table 1, in accordance with the permissible
limit of actual storage (see A.1.2.1).
Table 1 – Moisture soak conditions for non-dry-packed SMDs
Permissible limit on
Temperature Relative humidity Duration time
Condition
°C % h actual storage
A1 or B1
85 ± 2 85 ± 5 168 ± 24 <30 °C, 85 % RH
RH: Relative humidity
NOTE Conditions A1 and B1 indicate moisture soak for non-dry-packed SMDs under either method A or B.

5.3.3 Moisture soak for dry-packed SMDs
5.3.3.1 General
Moisture soak conditions for dry-packed SMDs may be used as specified in method A, Table 2,
or method B, Table 3. Moisture soak conditioning for dry-packed SMDs consists of two stages.
The first stage of conditioning is intended to simulate moisturizing SMDs before opening the
dry pack/dry cabinet. The second stage of conditioning is to simulate moisturizing SMDs during
storage after opening the dry pack for soldering (floor life). Moisture soak conditioning for dry-
packed SMDs shall be selected from method A or B. Method A shall be used when the relative
humidity in the dry pack or dry cabinet is specified by the manufacturer as being between 10 %
and 30 %. Method B shall be used when the relative humidity in the dry pack or dry cabinet is
specified by the manufacturer as being below 10 %.

60749-20 © IEC:2008 – 9 –
5.3.3.2 Method A
Unless otherwise detailed in the relevant specification, the first stage conditioning of A2, as
shown in Table 2, shall be performed. Subsequently, the second stage conditioning of A2, as
shown in Table 2, shall be performed within 4 h of finishing the first stage of conditioning (see
A.1.2.2).
The relative humidity of the first stage conditioning must be the same as the upper limit of the
relative humidity inside the moisture barrier bag. The relative humidity of the second stage
conditioning must be the same as the conditions of floor life.
Where required in the relevant specification, test conditions other than those of the moisture
barrier bag and floor life conditions may be specified in the moisture soak conditions of Table 2.
Table 2 – Moisture soak conditions for dry-packed SMDs (method A)
Permissible storage
Moisture soak conditions in the dry Condition of
Condition
conditions pack and the dry floor life
cabinet
A2 first-stage (85 ± 2) °C, (30 ± 5) % RH,
conditioning
<30 °C, 30 % RH, 1 year –
168 h
−0
A2 second-stage
(30 ± 2) °C, (70 ± 5) % RH,
conditioning
– <30 °C, 70 % RH, 168 h
168 h
−0
RH: Relative humidity
NOTE 1 The first stage of conditioning represents storage conditions in the dry pack and the dry cabinet, as well
as increasing relative humidity in the dry pack, by repacking the SMDs at the distributor's facility and the user's
inspection facility. When condition A2 is applied, the SMDs should be packed into a moisture-proof bag with IC
trays and desiccants within a few weeks of drying. They may then be subjected to multiple temporary openings of
the moisture-proof bag (for several hours at a time). Repack and inspection of SMDs are possible while the
humidity indicator in the dry pack indicates less than 30 % RH since SMDs will recover the initial condition of
absorbed moisture within a few days of repacking. In this case, the moisture content measurement of SMDs (see
Clause A.2) is not needed as a moisture control of the dry pack. A check of the moisture indicator is sufficient for
moisture control.
NOTE 2 When moisture soak of the first-stage conditioning does not result in saturation, the soak time is
extended to 336 h, because SMDs in a dry pack or dry cabinet will become saturated with moisture during long-term
storage. When moisture soak of the first stage of conditioning reaches saturation, the soak time is shortened.
5.3.3.3 Method B
The condition of moisture soak conditioning shall be selected from Table 3 in accordance with
the condition of the floor life detailed in the relevant specification (see A.1.2.3).

– 10 – 60749-20 © IEC:2008
Table 3 – Moisture soak conditions for dry-packed SMDs (method B)
Total conditions from baking
Condition Moisture soak conditions to dry packing and temporary Condition of floor life
opening of the dry pack
(85 ± 2) °C, (60 ± 5) % RH,
<30 °C, 60 % RH,
B2 <30 °C, 60 % RH, 24 h
+24
1 year
168 h
−24
(30 ± 2) °C, (60 ± 5) % RH,
<30 °C, 60 % RH,
B2a
<30 °C, 60 % RH, 24 h
+24
4 weeks
696 h
−24
(30 ± 2) °C, (60 ± 5) % RH,
B3 <30 °C, 60 % RH, 24 h <30 °C, 60 % RH, 168 h
+24
192 h
−0
(30 ± 2) °C, (60 ± 5) % RH,
B4 <30 °C, 60 % RH, 24 h <30 °C, 60 % RH, 72 h
+24
96 h
−0
(30 ± 2) °C, (60 ± 5) % RH,
B5
<30 °C, 60 % RH, 24 h <30 °C, 60 % RH, 48 h
+24
72 h
−0
(30 ± 2) °C, (60 ± 5) % RH,
B5a
<30 °C, 60 % RH, 24 h <30 °C, 60 % RH, 24 h
+24
48 h
−0
(30 ± 2) °C, (60 ± 5) % RH,
B6 <30 °C, 60 % RH, 6 h
+24
6 h
−0
RH: Relative humidity
NOTE 1 Moisture soak conditions from B2 to B6 consist of the first-stage conditioning (30 °C, 60 % RH, 24 h) and
the second-stage conditioning (floor life).
NOTE 2 Contents in the dry pack of SMDs, IC trays and other materials, should be fully dried just before packing
into the moisture-proof bag and the desiccant should be completely dry. This is because moist materials and
degraded desiccants give off water vapour, causing the relative humidity in the dry pack to exceed 10 %.
The relative humidity in the dry pack should be verified by the humidity indicator and the moisture content
measurement of the SMDs, as shown in Clause A.2.
NOTE 3 Storage of SMDs in a dry cabinet instead of a dry pack is not recommended because very low relative
humidity cannot be obtained in a dry cabinet.
NOTE 4 The individual conditions of method B should cover total storage condition from baking the SMDs to
soldering them, and this should include the duration time of room storage from baking the SMDs to packing them
into the dry pack, temporary opening of the dry pack and the floor life.
5.4 Soldering heat
5.4.1 General
Unless otherwise detailed in the relevant specification, the specimen shall be subjected to
soldering heat within 4 h of finishing the moisture soak or baking. The method and condition of
soldering heat shall be selected from 5.4.2 to 5.4.4 according to the relevant specification.
Whichever method is chosen, the soldering heat cycles shall be a minimum of one and a
maximum of three. Unless otherwise detailed in the relevant specification, one cycle of
soldering heat shall be used. If more than one cycle is selected, the specimen shall be cooled
down to below 50 °C before the second, and subsequent, soldering heat.

60749-20 © IEC:2008 – 11 –
NOTE If the specimen is not affected by moisture soak and drying, which takes place during room storage of over
4 h, a storage time exceeding 4 h following the completion of moisture soak or the baking may be detailed in the
relevant specification.
5.4.2 Method of heating by infrared convection or convection reflow soldering
5.4.2.1 Preparation
The specimen shall be put on the holder.
5.4.2.2 Preheating
Unless otherwise specified in the relevant specification, the specimen shall be preheated at a
temperature conditions range shown in A.3.1 for 60 s to 120 s in the reflow soldering apparatus.
5.4.2.3 Solder heating
Following preheating, the temperature of the specimen shall be raised to peak temperature and
then lowered to room temperature. The heating condition shall be selected from Table 4 or
Table 5 in accordance with the relevant specification depending on the actual soldering
conditions. Tolerances of temperature and time are shown in A.3.1.
NOTE 1 In Tables 4 and 5, the conditions of Method A are applied for actual soldering on condition of short
temperature profile, and the conditions of Method B are applied for actual soldering on condition of long
temperature profile.
NOTE 2 Following preheating, the temperature of the specimen should follow the values as indicated in the profile
given in Figure A.9, Figure A.10 or Table A.2.
Table 4 – SnPb eutectic process – Classification reflow temperatures
Temperature
Time within 5 °C of
for volume
Package specified
mm
thickness Method classification
350 – ≥ 2 000
mm <350
temperature
°C 2 000 °C
s
°C
Method A 10 240 240 225
< 2,5
Method B 20 240 225 225
≥ 2,5 Method A 10 240 240 225
Method B 20 225 225 225
– 12 – 60749-20 © IEC:2008
Table 5 – Pb-free process – Classification reflow temperatures
Package Method Time within 5°C of the Temperature for volume
thickness specified classification mm

mm temperature
<350 350 – 2 000 >2 000
s
°C °C
°C
Method A 10 260 260 260
<1,6
Method B 30
1,6 – 2.5 Method A 10 260 250 245
Method B 30
>2,5 Method A 10 250 245 245
Method B 30
5.4.3 Method of heating by vapour-phase reflow soldering
5.4.3.1 Preparation
The specimen shall be put on the holder.
5.4.3.2 Preheating
Unless otherwise specified in the relevant specification, the specimen shall be preheated at a
temperature from 100 °C to 160 °C for 1 min to 2 min in the vapour-phase soldering apparatus.
5.4.3.3 Solder heating
The temperature of the specimen shall be raised after preheating. When the temperature of the
specimen has reached 215 °C ± 5 °C, it shall be maintained for 40 s ± 4 s as shown in Table 6
(refer to A.3.2).
Table 6 – Heating condition for vapour-phase soldering
Temperature Time
Condition
°C s
II-A 215 ± 5 40 ± 4
5.4.4 Method of heating by wave-soldering
5.4.4.1 Preparation
The bottom surface of the specimen shall be fixed to the holder by an adhesive agent specified
in the relevant specification. Unless otherwise detailed in the relevant specification, flux shall
not be applied to the specimen and holder.
NOTE 1 If flux is applied, vaporization of solvent in the flux could affect the temperature rise of the specimen. Flux
should not, therefore, be applied to the body of the specimen and should only be applied to lead pins as sparingly
as possible.
60749-20 © IEC:2008 – 13 –
NOTE 2 Where SMDs have a stand-off (height between the bottom of the SMD body and the bottom of the lead
pin) of less than 0,5 mm (except lower thermal resistance SMDs with a heat sink and whose body thickness
exceeds 2,0 mm), they should be tested by soldering heat of methods A and B. SMDs whose body thickness
exceeds 3,0 mm are tested by soldering heat by condition I-B. Wave-soldering of conditions III-A and III-B should
be omitted because methods A and B are more severe than conditions III-A and III-B for these SMDs (refer to
A.3.3).
5.4.4.2 Preheating
Unless otherwise detailed in the relevant specification, the specimen shall be preheated at a
temperature of 80 °C to 140 °C for 30 s to 60 s in the soldering apparatus.
5.4.4.3 Solder heating
Following preheating, the specimen and the holder shall be immersed into flowing molten
solder, as shown in Figure 2. The immersion condition shall be selected from Table 7.
Flowing molten
Holder
solder
Direction
Specimen Direction
IEC  1747/01 IEC  1748/01
Figure 2a – Start of immersion Figure 2b – End of immersion
Figure 2 – Heating by wave-soldering
Table 7 – Immersion conditions for wave-soldering
Temperature of solder Immersing time Actual soldering
Condition
°C s method
III-A Single-wave
260 ± 5 5 ± 1
III-B Double-wave
260 ± 5 10 ± 1
5.4.4.4 Cleaning
If the flux is applied, it shall be removed by a cleaning method detailed in the relevant
specification.
5.5 Recovery
If recovery is detailed in the relevant specification, the specimen shall be stored under
standard atmospheric conditions for the time given in the specification.
NOTE Wave-soldering is not commonly available to the semiconductor manufacturer. Where the manufacturer
does not have access to such equipment, the method should be specified only by agreement between the
manufacturer and the customer.

– 14 – 60749-20 © IEC:2008
5.6 Final measurements
5.6.1 Visual inspection
Visual inspection, as specified in IEC 60749-3, shall be performed after the test. Special
attention shall be paid to external cracks and swelling which will be looked for under a
magnification of 40×.
5.6.2 Electrical measurement
Electrical testing shall be performed as required by the relevant specification.
5.6.3 Internal inspection by acoustic tomography
Unless otherwise specified in the relevant specification, internal cracks and delamination in the
specimen shall be inspected by acoustic tomography in accordance with IEC 60749-35.
6 Information to be given in the relevant specification
Subclause
a) Material of holder 4.3
b) Position of specimen on the holder 4.3
c) Composition of flux 4.6
d) Number of test specimens 5
e) Item and failure criteria for initial measurement 5.1
f) Preconditioning 5.2
g) Method of moisture soak 5.3
h) Conditions of drying 5.2
i) Baking conditions instead of the moisture soak 5.3
j) Method of moisture soak for dry packed SMDs 5.3.3
k) Period between the stages of moisture soak conditioning 5.3.3.2
l) Conditions of first-stage and second-stage conditioning
and whether another condition is needed 5.3.3.2
m) Soak time of the first-stage conditioning if 168 h of soak time 5.3.3.2
is insufficient
n) Moisture soak conditions for SMDs stored in completely 5.3.3.3
dried dry pack
o) Moisture soak conditions for non-dry-packed SMDs 5.3.2
p) Period between finish of moisture soak and soldering heat 5.4.1
q) Method and condition of soldering heat 5.4.1
r) Number of cycles of soldering heat 5.4.1
s) Preheat conditions for infrared convection and convection 5.4.2.2
reflow soldering
t) Heating conditions for infrared convection and convection 5.4.3.3
reflow soldering
u) Preheat conditions for vapour-phase reflow soldering 5.4.3.2
v) Adhesion method 5.4.4.1
w) Preheat conditions for wave-soldering 5.4.4.2

60749-20 © IEC:2008 – 15 –
x) Cleaning method for flux 5.4.4.4
y) Recovery conditions 5.5
z) Item and failure criteria for final measurement 5.6

– 16 – 60749-20 © IEC:2008
Annex A
(informative)
Details and descriptions of test method on resistance
of plastic encapsulated SMDs to the combined effect of moisture
and soldering heat
A.1 Description of moisture soak
A.1.1 Guidance for moisture soak
Method A and method B of moisture soak of 5.3 are intended to be used for dry-packed SMDs,
whereas the conditions in Table 1 are intended for use with non-dry-packed SMDs which have
been stored under room conditions.
Where package cracking is generated by soldering heat after the moisture soak of conditions
found in Table 1, it is recommended that devices be dry-packed or stored in a dry atmosphere.
If the cracking is generated by solder heating after the moisture soak of method A and
method B, it is recommended that SMDs be pre-baked before being soldered on to the PCBs.
A.1.2 Considerations on which the condition of moisture soak is based
A.1.2.1 General description of moisture soak
The presence of moisture in SMDs is caused by diffusion of water vapour into the resin. The
moisture content of the resin needs to be examined, since package cracking during soldering
emanates from near the die pad or the die. Examples of characteristics for moisture soak at
85 °C, 85 % relative humidity, are shown in Figure A.1. In the case where the resin thickness
from the bottom surface of the package to the die pad is 1 mm, Figure A.1 indicates that over
168 h are needed for saturation to take place.
Moisture soak characteristics, such as that of the resin in Figure A.3, show a slow moisture
soak speed which is nevertheless considered significant. Figure A.1 and Figures A.4 to A.8
represent moisture soak characteristics of the resin.
Saturation is needed for soldering heat tests in order to simulate long-time storage of, for
example, one year which occurs when SMDs are dry-packed or warehoused. The diffusion
speed of water vapour into resin depends only on temperature. Given the resin thickness as
defined in Figure A.2, saturating moisture time at 85 °C depends on the resin thickness
as shown in Figure A.3. It would appear that, for a normal SMD whose resin thickness is
from 0,5 mm to 1,0 mm, 168 h of moisture soak time are required.

60749-20 © IEC:2008 – 17 –
The saturated moisture content of resin depends on temperature and relative humidity as
shown in Figure A.4. The relative humidity required for moisture soak can be determined from
Figure A.4 (for example, so that the content of moisture at 85 °C can be made to correspond
with the content of moisture at 30 °C, the actual storage temperature). Conditions of moisture
soak for soldering heat tests are derived from Figure A.4 as shown in Table A.1.
Figure A.5 shows the moisture content in resin at the first interface (top surface of die or
bottom surface of die pad) under conditions of moisture soak and real storage conditions.
168 h
72 h
48 h
24 h
0 8 h
0,2 0,4 0,6 0,8 1
Back surface of SMD Die pad
Distance from back surface of SMD  mm
IEC  1749/01
Figure A.1 – Process of moisture diffusion at 85 °C, 85 % RH

Die
Resin
a
b
Die pad
IEC  1750/01
NOTE “a” or “b”: the thicker of the two is defined as the resin thickness and the top surface of the die or the
bottom surface of the die pad is defined as the first interface.
Figure A.2 – Definition of resin thickness and the first interface

Moisture content
of resin  mg/cm
– 18 – 60749-20 © IEC:2008
0,5
0 1 1,5
Resin thickness  mm
IEC  1751/01
Figure A.3 – Moisture soak time to saturation at 85 °C
as a function of resin thickness
Storage Moisture soak
conditions conditions
at 30 °C at 85 °C
100 % RH
Table 1
Condition B2
50 % RH
Condition A2
30 % RH
0 20 40
Temperature °C
IEC  2201/08
Figure A.4 – Temperature dependence of saturated moisture content of resin
Table A.1 – Comparison of actual storage conditions
and equivalent moisture soak conditions before soldering heat
Relative humidity for moisture
Condition Actual conditions of storage soak at 85 °C
%
A2 30 °C max., 30 % RH max.
30 ± 5
Table 1 30 °C max., 85 % RH max. 85 ± 5
B2 30 °C max., 60 % RH max.
60 ± 5
Saturated moisture content
Time for moisture content of resin
of resin  mg/cm
at the first interface to reach 95 %  h

60749-20 © IEC:2008 – 19 –
85 °C, 85 % RH, 168 h
30 °C, 85 % RH, 1 year
85 °C, 60 % RH, 168 h
30 °C, 60 % RH, 1 year
85 °C, 30 % RH, 168 h
30 °C, 30 % RH, 1 year (storage condition in dry pack)
0 0,5 1,5
Resin thickness  mm
IEC  1753/01
Figure A.5 – Dependence of moisture content of resin at the first interface
on resin thickness under various soak conditions
A.1.2.2 Moisture soak conditioning – Method A
Method A of moisture soak given in item 5.3.3.2 is based on conditions where SMDs are stored
in a dry pack or dry cabinet for a long time, under permissible conditions of 30 °C, 30 % RH, for
one year, and where the packing/cabinet can be opened temporarily any number of times for a
few hours at a time, provided the humidity indicator indicates below 30 % RH.
Figure A.6 shows that the first-stage conditioning A3 and the second-stage conditioning A2
completely represents a floor life of 30 °C, 70 % RH, 168 h after opening the dry pack even
though the dry pack is degraded into a condition of 30 % RH.

Moisture content of resin at first interface
after moisture soaking  mg/cm

– 20 – 60749-20 © IEC:2008
30 °C, 70 % RH, 168 h after moisture
soak of 85 °C, 30 % RH, saturation
(condition A3 after condition A2)
30 °C, 70 % RH, 168 h after
opening the dry pack
85 °C, 30 % RH, saturation
level
30 °C, 30 % RH, 1 year (condition of the dry pack)
0 0,5 1,0 1,5
Resin thickness  mm
IEC  1754/01
Figure A.6 – Dependence of moisture content of resin at the first interface
on resin thickness related to method A of moisture soak
A.1.2.3 Moisture soak conditioning – Method B
Method B of moisture soak given in 5.3.3.3 is based on conditions where SMDs, IC trays and
other materials have been completely baked immediately before dry packing and the volume of
dried desiccant added to the enclosure bag ensures absorption of moisture diffused through
the enclosure bag. Integrity of the dry pack is verified through
a) use of in situ moisture control indicators of a sensitivity that will alert for loss of enclosure
bag integrity; and
b) determination of SMD moisture content as shown in Clause
...