IPC-TM-650 EN 2022 试验方法.pdf - 第277页
5.1.2 Rinse the coupon with deionized water, then dry the coupon. 5.2 Test 5.2.1 Immerse the coupon in the liquid flux at room tem- perature to a minimum depth of 10.0 mm [0.394 in]. 5.2.2 Immediately drain off excess fl…
1
Scope
This
test method assesses the relative activity of
liquid fluxes using a wetting balance.
2
Applicable Documents
ISO 1634
IPC J-STD-004
Requirements
for Soldering Fluxes
3
Test Specimen
3.1
The
test specimen shall be a copper coupon complying
with ISO 1634-CU-ETP Condition HA. The width shall be 6.0
± 0.25 mm [0.236 ± 0.00984 in]; the length should be 25.0 ±
1.0 mm [0.984 ± 0.0394 in] or as appropriate to the test
equipment. The thickness shall be 0.5 ± 0.05 mm [0.0197 ±
0.00197 in].
3.2
A
minimum of 50 ml of the liquid flux to be tested.
4
Apparatus and Reagents
4.1 Apparatus (see Figure 1).
4.2
A
meniscus force measuring device (wetting balance)
which includes a temperature-controlled solder pot containing
solder maintained at 245 ± 3 °C [473 ± 5.4 °F].
Note: Reaction rate is very sensitive at this temperature.
Solder composition shall be Sn60/Pb40 or Sn63/Pb37.
4.3
A
chart recorder, data logger, or computer capable of
recording force as a function of time with a minimum recorder
speed of 10 mm/s [0.394 in].
4.4
A
mechanical dipping device able to produce an immer-
sion and emersion rate of 20-25 mm [0.787-0.984 in] per
second to a depth of 6.0 ± 0.1 mm [0.236 ± 0.00394 in], with
a dwell time of 5.0 ± 0.5 seconds.
5
Procedure
5.1 Preparation
5.1.1
Degrease
the test coupon by immersing it in a suitable
solvent. Use a 10 ± 1% fluoroboric acid dip to clean the cou-
pon.
IPC-24142-1
Figure
1 Wetting Balance Apparatus
▼
▼
Chart
Recorder
Signal
Conditioner
Controls
Solder
Bath
Heater
Clamp
Copper
Coupon
Relative
Motion
LVDT
(Transducer)
▼
2215
Sanders Road
Northbrook, IL 60062-6135
IPC-TM-650
TEST
METHODS MANUAL
Number
2.4.14.2
Subject
Liquid
Flux Activity, Wetting Balance Method
Date
06/04
Revision
A
Originating Task Group
Flux Specifications Task Group, (5-24a)
Material
in this Test Methods Manual was voluntarily established by Technical Committees of IPC. This material is advisory only
and its use or adaptation is entirely voluntary. IPC disclaims all liability of any kind as to the use, application, or adaptation of this
material. Users are also wholly responsible for protecting themselves against all claims or liabilities for patent infringement.
Equipment referenced is for the convenience of the user and does not imply endorsement by IPC.
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5.1.2
Rinse
the coupon with deionized water, then dry the
coupon.
5.2
Test
5.2.1
Immerse
the coupon in the liquid flux at room tem-
perature to a minimum depth of 10.0 mm [0.394 in].
5.2.2 Immediately
drain off excess flux by standing the
specimen vertically on a clean filter paper for 1-5 seconds.
5.2.3
After
partial drying, mount the coupon in the test
equipment.
5.2.4
Skim
(remove dross from) the surface of the molten
solder just prior to immersing the specimen in the solder.
5.2.5
Hold
the specimen 3.0 mm [0.118 in] above the sol-
der pot for approximately 10 ± 1 seconds. Start the test.
Immerse the specimen to a depth of 5.0 ± 0.1 mm [0.197 ±
0.00394 in], using an immersion and emersion rate of 20-25
mm [0.787-0.984 in] per second and a dwell time of 5.0 ± 0.5
seconds.
5.2.6
Record
the wetting curve during the test.
5.3
Evaluation
Use
the wetting balance curve recorded
during the test to determine the following flux activity param-
eters:
5.3.1
Tw,
the wetting time. This is the time at which the
wetting curve crosses the corrected zero axis, measured from
the start of the test (see Figure 2).
5.3.2
The
maximum wetting force, Fmax, with the zero axis
corrected for buoyancy (see 6.2 and Figure 2).
6
Notes
This
test method can be useful in requalifying
materials that have exceeded the recommended shelf life. In
IPC-24142-2
Figure
2 Wetting Balance Curve
TIME
▼
FORCE (
µ
N)
▼
0
▼
▼
▼
Instrument Zero
Corrected Zero
Fmax
T
w
IPC-TM-650
Number
2.4.14.2
Subject
Liquid
Flux Activity, Wetting Balance Method
Date
06/04
Revision
A
P
age2of3
电子技术应用 ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ
addition,
the method can help evaluate fluxing power on criti-
cal applications prior to manufacturing operations.
6.1
Safety
Observe all appropriate precautions on MSDS
for chemicals involved in this test method.
6.2
Correction for Buoyancy
For the results from different
wetting balance tests to be relatable, it is necessary to correct
for the variability in specimen sizes. This is done by correcting
the zero axis for the buoyant force produced by the volume of
sample immersed in the solder. (The instrument zero corrects
for the weight of the specimen.) The following formula is used
to calculate the magnitude of the buoyant force correction,
P
b
,
in µN: P
b
= ρ gV
Where:
ρ =
Density of solder @ 245°C (8.15g/cm
3
)*
g
= Acceleration of gravity (9810 mm/s
2
[386.220
in/
2
])
V
= Immersed volume of coupon (cm
3
)
v
= width x thickness x immersion depth)
*For Sn60/Pb40 Alloy
The calculated buoyancy force must be used to correct the
zero axis. This correction is required to obtain correct values
of wetting times as well as wetting forces. All measurements
of wetting times and wetting forces must be made from the
corrected zero axis. In the case of an upright (tensile force)
curve, the corrected zero axis will be below the instrument
zero, as shown in Figure 2.
Note: The vertical (tensile) force measured by the wetting bal-
ance consists of three forces – the weight of the specimen,
the buoyancy force, and the wetting force caused by the sur-
face tension of the solder and its interaction with the fluxed
coupon.
The weight of the specimen is constant, and is included in the
instrument zero axis.
The buoyancy force is equal to the weight of the solder dis-
placed when the specimen is immersed. It changes as the
specimen is lowered into and removed from the solder, but
may be considered constant during the dwell time.
The only changing force during the dwell time is the wetting
force. Changes in this force are caused by the contact angle
changing from initial nonwetting to wetting, as the specimen
solders. The corrected zero (buoyancy) line is the force when
the contact angle is 90°, or when the bath surface has
returned to horizontal, having been initially depressed by the
immersed sample. When the contact angle is 90°, the contri-
bution of the wetting force to the total vertical force is 0.
The wetting balance curve is centered on the corrected zero
(buoyancy) line, since the only parameter that changes during
the test dwell time is the contact angle, θ. The measured ver-
tical tensile force, F, in µN (omitting the constant weight of the
specimen, which is zeroed out by the instrument), is given by:
F=γρcos θ -gρv
Where:
γ = Surface tension of molten solder (400 µN/mm)
p = Specimen perimeter in mm
θ = Contact angle
g = Gravitational acceleration (9.81 x 10
3
mm/s
2
)
ρ =
Solder density (~8000 µg/mm
3
)
v
= Immersed volume in mm
3
The
buoyancy is the value of F when θ is 90° (cos θ = 0):
Buoyancy = -gρv
The corrected zero line (buoyancy) is the fixed reference point
for wetting force and wetting time measurements.
Altering the specimen dimensions changes the immersed vol-
ume and hence the buoyancy, and so alters the position of
the corrected zero line; but the wetting curve still remains
centered on this line. Similarly, any change in immersion depth
will also alter the immersed volume, with the same effect on
the buoyancy.
Although use of the corrected zero line will cancel small varia-
tions in the specimen immersed volume and the immersion
depth, large changes will affect the rate of heat transfer into
the specimen, which will affect both Tw, the time to recross
the corrected zero (buoyancy) line, and the time to reach
Fmax.
IPC-TM-650
Number
2.4.14.2
Subject
Liquid
Flux Activity, Wetting Balance Method
Date
06/04
Revision
A
P
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