Solder paste, also known as solder paste, is a technology associated with surface filming
(Surface Mount Assembly,
AbbreviationSMT)
And the new welding materials produced. Its main function is to form solder joints in components and boards to connect metals. Solder paste is a non-Newtonian fluid whose composition and quality can be reflected by viscosity. In solder paste printing, different types of printing techniques andPCB
The thickness of the printed board on the board is highly dependent on the optimum solder paste viscosity value, so accurate solder paste viscosity values ​​are important in solder paste printing. The solder paste viscometer is mainly used to measure the viscosity value of the solder paste liquid. It uses a rotary pump sensor and a built-in coaxial double cylinder. It is a liquid viscosity physical analysis instrument. It measures viscosity in industrial production. To monitor the composition and quality of the substance. Therefore, solder paste viscometers require periodic calibration to ensure the accuracy and stability of their measurements. For the calibration of solder paste viscometer, refer to the national instrument metrology verification procedure.JJG1002-2005
Rotational viscometer verification procedures.1
Instrument measurement method
1.1
Measurement basis
according to"
JJG1002-2005
Rotational viscometer verification procedure, solder paste viscometerInstrument measurement
The relative method is used, that is, the standard solution is measured using a viscometer.
(
The main component is silicone oil)
A method of comparing viscosity values ​​to standard values.1.2
Viscosity measurement
Since the change in temperature has a great influence on the viscosity of the solution, it is in the rotary viscometer.
Instrument calibration
The indoor temperature and temperature conditions during the process are
20
±1
°C, relative humidity is not greater than65%
. Before performing the test, the inner cylinder, outer cylinder and viscosity cup of the solder paste viscometer rotor should be ultrasonically cleaned and ensured to be dry and clean before use.The solder paste viscometer is placed on a horizontal work surface and the glass containing the standard viscosity liquid is placed in the cup. Turn on the viscometer power switch and adjust its indication value in case of idling
000.0
By arranging the up and down movement buttons, the rotor is immersed in the standard viscosity liquid so that the liquid surface is at the sensor discharge port.5~10mm
At the speed, the speed is set to10rpm
, the temperature is set to20
°C. The temperature value of the instrument dial is20
Press the start-up operation at °C until the reading is stable and record the measured value. Measure under the same conditions10
And record the measurement results.2
, uncertainty sources and analysis
2.1
mathematical model
y(
η
)=f(Ka)
Η——the power of the standard liquid at a specific temperature;
K
- viscometer constant;A
- Deflection angle.
Since the individual inputs are independent of each other, the relative standard uncertainty is:
2.2
Uncertain source analysis
The factors affecting the measurement results include: the uncertainty caused by the repetitive measurement; the uncertainty caused by the indication error of the platinum resistance temperature measurement; the uncertainty caused by the resolution of the instrument display; the uncertainty caused by the standard solution setting, such as Figure
1
Shown as follows:
2.3
Measurement uncertainty assessment
2.3.1
Measuring the uncertainty caused by repeatability
u r
Viscosity value
13.8Pa
·s -1
The standard viscosity liquid is measured ten times, and the measured results and environmental recording conditions are as follows.1
:Calculate the average based on the experimental results measured in the table
x
for13.78Pa
·s -1
The residuals of each measurement are:-0.12Pa
·s -1
,0.12Pa
·s -1
,0.02Pa
·s -1
,0.08Pa
·s -1
,0.02Pa
·s -1
,0.08Pa
·s -1
,-0.18Pa
·s -1
,-0.18Pa
·s -1
,-0.08Pa
·s -1
,-0.02Pa
·s -1
, using the Bezier formula to calculate the standard deviation:
2.3.2
Uncertainty caused by thermometer measurement error
u t
A platinum resistance thermometer is used in the calibration process of the instrument, and the index is
0.1
°C, because the limit error cannot exceed the minimum index3
Times, temperature change1
The change in viscosity caused by °C is average3%
, calculation by repeatability results13.78Pa
·s -1
×3%=0.4134Pa
·s -1
.JJG1002-2005
The temperature fluctuations required in the test do not exceed0.1
°C, the resulting maximum viscosity change is0.4134
×0.1=0.04134Pa
·s -1
.,
uncertaintyu t
for:
2.3.3
Calculation shows the uncertainty introduced by resolution
u s
The numerical value of the scale value is
d=0.1Pa
·s -1
, display resolution is1d
Since the uncertainty caused by such errors is the quantitative uncertainty of the electronic counter, it is subject to uniform distribution.,
uncertaintyu s
for:
2.3.4
Standard viscosity liquid setting uncertainty
u l
The viscosity of the standard viscosity liquid is generally half a year, and the viscosity value will change slightly during the period from the preparation to the use.
JJG1002-2005
Permissible error requirements are given in the Rotational Viscometer Calibration Procedure0.1%
~0.5%
With maximum tolerance0.5%
Calculate, calculate the uncertainty introduced by the standard solution according to the uniform distributionu 1
:
2.5
Synthetic standard uncertainty
u c
And extended uncertainty
3
Conclusion
Solder paste viscometer
Instrument calibration
The process is affected by many factors. According to the calculation result of uncertainty, the influence of relevant factors can be minimized, and the quality of instrument calibration work can be improved.
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