JPH08242073A - Cream solder printing method - Google Patents

Abstract

PURPOSE: To provide a cream solder printing method which eliminates poor soldering caused by printing. CONSTITUTION: In the title cream solder printing method, a temperature control range of cream solder 4 is calculated in advance from viscosity characteristic of the cream solder 4, a moving print-rate of a squeezee 3 during cream solder print, an opening width and a thickness of a screen mask plate 1 and an allowable amount of slump of cream solder after printing and the occurrence of defective print is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cream solder printing method for printing and applying cream solder to a printed circuit board.

[0002]

2. Description of the Related Art In recent years, a technique for mounting electronic components on a printed circuit board has been developed. -High-precision printing that applies and prints in a prescribed shape is required. The solder temperature is an important factor that determines the quality of these printings. Conventionally, as a solder temperature control standard, for example, the temperature (25 C.) or by actually confirming the change in the printing environment by experiments, and empirically determining the allowable solder temperature based on the results.

[0003]

However, in the conventional cream solder printing method, it is necessary to experimentally confirm the solder temperature determination for various cream solders in advance. Further, the amount of solder drool after cream solder printing is influenced by printing parameters such as the squeegee speed during cream solder printing, the opening width and thickness of the screen mask plate, and the printing ambient temperature during cream solder printing, in addition to the solder temperature. Therefore, it is necessary to spend an enormous amount of time just to confirm the experiment beforehand.

Further, the above-mentioned printing parameters can be repeatedly obtained with stable reproduced values by a cream solder printing machine or a temperature controller such as an air conditioner, but the viscosity value of the cream solder is changed by the shearing force repeatedly applied during the printing operation. Since the viscosity value of the cream solder to be used, that is, the viscosity changes, printing with the same print parameter setting value cannot be suppressed within the range of the predetermined allowable solder dripping amount.

Therefore, according to the present invention, the amount of solder dripping after cream solder printing is determined in advance from printing parameters such as the squeegee speed during cream solder printing, the opening width and thickness of the screen mask plate, and the printing ambient temperature during cream solder printing. Provided is a cream solder printing method for calculating a cream solder dripping amount and determining a condition for suppressing it within a predetermined allowable solder dripping amount range.

[0006]

In order to solve the above problems, the present invention provides a cream solder printing method in which cream solder is printed and applied to a printed circuit board by using a screen mask plate and a squeegee. From the relationship between the temperature gradient and the speed gradient (shear speed), the opening width of the screen mask plate that fills the cream solder, the squeegee movement printing speed at the time of filling, the printing thickness after cream solder printing, and the allowable amount of solder dripping for the specified printing width, A cream solder printing method is characterized in that an allowable temperature of cream solder is calculated.

[0007]

According to the above-mentioned method of the present invention, when it is considered that gravity acts on the cream solder printed on the printed circuit board to cause the printed shape to sag, the cream solder is calculated from the allowable solder dripping amount for the designated printing width. Allowable temperature, the allowable opening width of the screen mask plate, the allowable squeegee movement printing speed at the time of filling, calculate the allowable print thickness after cream solder printing, especially among the soldering defects due to cream solder printing,
Since it is possible to prevent the occurrence of solder bridging due to printing bleeding in advance, it is not necessary to check many experiments and repeat failures.

Further, even if the viscosity value of the cream solder changes due to the shearing force repeatedly applied during the printing operation, the print parameter setting value can be sequentially calculated and set to the optimum value, so that the width after the cream solder printing is performed. Can be suppressed within a range of a predetermined allowable amount of solder drool.

[0009]

EXAMPLE A cream solder printing method according to an example of the present invention will be described. FIG. 1 is a configuration diagram of a cream solder printing apparatus according to an embodiment of the present invention, FIG. 2 is a diagram showing a printing cross-sectional shape after cream solder printing, and FIG. 3 is a squeegee in the opening of a screen mask plate for soldering the cream solder. FIG. 4 is a diagram showing a filling process of cream solder to be filled. FIG. 4 is a diagram showing viscosity (viscosity coefficient η) of cream solder, velocity gradient (shear velocity D),
It is a figure which shows the relationship of temperature T.

In FIG. 1, as components, 1 is a screen mask board, 2 is a printed circuit board, 3 is a squeegee,
Reference numeral 4 is a cream solder, 5 is a stage supporting the printed circuit board 2 from below, and 6 is an air conditioner for controlling the temperature of the entire printing system.

In FIG. 2, 7 indicates the cream solder after printing-filling-separation, H in the figure is the printing height immediately after the printing of the cream solder, and V _H is the sagging speed of the cream solder. In FIG. 3, 8 is the opening of the screen mask plate 1, t is the thickness of the screen mask plate 1, W is the opening width of the screen mask plate 1, and V is the moving speed of the squeegee 3.

Next, the operation of cream solder printing will be described. The printed circuit board 2 is lifted by the stage 5 and brought into contact with the screen mask plate 1.
While scraping and moving the cream solder 4 supplied on the screen mask plate 1 shown in FIG. 3 (a) with the squeegee 3, it enters the opening 8 provided in the screen mask plate 1 as shown in FIG. 3 (b). The cream solder 4 is put in, and finally the cream solder 4 is filled in the opening 8 as shown in FIG.

As shown in FIG. 2, in the cream solder after printing-filling-separation, the pressure inside the cream solder generated by gravity acts as a shearing stress, so that the droop of the cream solder as shown by the arrow in the figure. Occurs. In addition, H in the figure
Shows the cream solder printing thickness on the vertical axis y of the printed circuit board 2. The state of this solder drooling speed is expressed by Equation 1 as shown by the equation.

[0014]

[Equation 1]

Where y is the vertical axis of the printed circuit board,
H is the print thickness of the cream solder, v is the solder dripping speed, η is the cream solder viscosity, ρ is the cream solder density, and g is the acceleration of gravity.

It should be noted that the opening width W of the screen mask plate, the thickness t, and the squeegee moving speed V are squeegees, and the equation for giving the speed gradient (shear speed D) when the cream solder is filled in the opening is become.

[0017]

[Equation 2]

In FIG. 2, the y axis is taken vertically above the printed circuit board 2, and the thickness dy and the area s are located at the height y.
Consider the following small volume. The gravity acting on this portion is given by Equation 3 when the density ρ of the cream solder is used.

[0019]

(Equation 3)

If the pressure acting from the lower surface of this portion is p and the pressure acting from the upper surface is p + dp, the equation of the balance in the vertical direction is given by

[0021]

[Equation 4]

Therefore,

[0023]

(Equation 5)

If the pressure at y = H is po and the pressure at an arbitrary height y is p, then ρ is constant.

[0025]

(Equation 6)

[0026] Further, when the relative velocity difference between the upper layer and the lower layer of the minute volume having the thickness dy is dr and the viscosity coefficient of the cream solder is η, the force F required to move the upper layer is expressed by Formula 7.

[0027]

(Equation 7)

When the pressure p at an arbitrary height y acts as the force F, dripping of the cream solder occurs. The number 6
From Equation 7, Equation 8 is obtained, and Equation 9 is obtained from this.

[0029]

(Equation 8)

[0030]

[Equation 9]

When the equation 9 is integrated and the boundary condition y = 0, the equation 10 is obtained from v = 0.

[0032]

[Equation 10]

By substituting the value of y into this, the above-mentioned equation 1 is obtained. Next, a method of obtaining the viscosity coefficient η of cream solder will be described. The viscosity coefficient η of cream solder can be measured in advance using a viscometer. However, as can be seen from the viscosity measurement result of the RA type cream solder shown in FIG. 4, the viscosity coefficient η changes depending on the velocity gradient (shear velocity) D and the temperature of the cream solder at that time.

Then, a method of obtaining the velocity gradient (shear velocity) D will be described. As described above, the viscosity of the cream solder, which is related to the sag of the cream solder, is determined by the shear rate of the cream solder during the process of filling the cream solder into the openings of the screen mask plate. As shown in FIG. 3, when the squeegee 3 moves the cream solder 4 on the screen mask plate 1 at the speed V, inside the mask opening,
The cream solder is filled as the squeegee 3 passes.

That is, the mask opening is filled with cream solder during the time W / V during which the squeegee 3 passes through the mask opening width W. At this time, the average cream solder filling speed in the vertical direction is given by Equation 11 since the mask thickness t is filled in W / V time.

[0036]

[Equation 11]

Therefore, as the velocity gradient D, from the definition, the formula 12 is obtained by substituting the formula 11 into the d (solder filling average speed) / dw.

[0038]

(Equation 12)

Here, an actual numerical value is applied to calculate the upper limit of the allowable solder temperature of cream solder. The following numerical values are applied as the print model. Cream solder: MR-7123 (RA type normal residue) Cream solder temperature: T ° C. Squeegee moving speed: V = 30 mm / s Mask opening width: W = 0.2 mm Mask plate thickness: t = 0.15 mm Cream solder density: ρ = 4.857 * 10 ³ kg
/ M ³ Gravity acceleration: g = 9.80665 m / s ² Cream solder printing thickness: H = 1.5 * 10 ⁻⁴ m Cream solder viscosity coefficient: η (* 10 Pa · s) Velocity gradient (shear velocity): D ( s ^-1 ) Allowable solder drooling speed: v≤0.02 mm / s From number 2 Velocity gradient (shear speed) D = 225 (s ^-1 ) From number 1 Cream when solder drooling velocity v = 0.02 mm / s Calculating the solder viscosity coefficient, η = 26.79 * 1
0 Pa · s Therefore, from FIG. 4, in the velocity gradient of the print model,
In order to print within the allowable solder drooling speed, the temperature of the cream solder must be maintained at a temperature at which the cream solder viscosity of point A or higher is obtained. Therefore, the upper limit of the allowable solder temperature at this time is 24 ° C.

[0040]

As is clear from the description of the above embodiment,
According to the present invention, the amount of solder drool after cream solder printing is calculated in advance from printing parameters such as the squeegee moving speed during cream solder printing, the opening width and thickness of the screen mask plate, and the printing ambient temperature during cream solder printing. It is possible to calculate the amount of sagging and determine in advance a condition for suppressing the amount of solder within a predetermined allowable range. by this,
By obtaining a good cream solder print shape, it is possible to eliminate soldering defects due to printing.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a cream solder printing apparatus as an embodiment to which the present invention is applied.

FIG. 2 is a diagram showing a print cross-sectional shape after cream solder printing.

FIG. 3 is a diagram showing a cream solder filling process.

FIG. 4 is a diagram showing the relationship between viscosity, speed gradient, and temperature in cream solder.

[Explanation of symbols]

 1 Screen Mask Plate 2 Printed Circuit Board 3 Squeegee 4 Cream Solder 5 Stage Supporting the Board from Below 6 Air Conditioner 7 Printing-Filling-Cream Solder After Plate Separation 8 Screen Mask Plate Opening

Claims (4)

[Claims] 1. In a cream solder printing method for printing and applying cream solder to a printed circuit board using a screen mask plate and a squeegee, the relationship between the viscosity coefficient of the cream solder, the velocity gradient (shear speed) and the temperature, and the cream solder filling. Cream solder printing characterized by calculating the allowable temperature of cream solder from the opening width of the screen mask plate, the squeegee movement printing speed during filling, the printing thickness after cream solder printing and the allowable amount of solder dripping for the specified printing width. Method. 2. In a cream solder printing method of printing and applying cream solder to a printed circuit board using a screen mask plate and a squeegee, the relationship between the viscosity coefficient of cream solder, the velocity gradient (shear rate) and temperature, and the cream solder filling. Calculate the allowable opening width of the screen mask plate to be filled with cream solder from the opening width of the screen mask plate, the squeegee movement printing speed during filling, the printing thickness after cream solder printing, and the allowable amount of solder drop for the specified printing width. A solder paste printing method characterized by: 3. A cream solder printing method of printing and applying cream solder to a printed circuit board using a screen mask plate and a squeegee, the relationship between the viscosity coefficient of the cream solder, the velocity gradient (shear rate) and the temperature, and the cream solder filling. It is characterized by calculating the allowable squeegee movement printing speed during cream solder filling from the opening width of the screen mask plate, the squeegee movement printing speed during filling, the printing thickness after cream solder printing, and the allowable amount of solder drool for the specified printing width. And the solder paste printing method. 4. In a cream solder printing method of printing and applying cream solder to a printed circuit board using a screen mask plate and a squeegee, the relationship between the viscosity coefficient of the cream solder, the velocity gradient (shear rate) and the temperature, and the cream solder filling. It is characterized in that the allowable printing thickness after cream solder printing is calculated from the opening width of the screen mask plate, the squeegee movement printing speed during filling, the printing thickness after cream solder printing and the allowable solder droop amount for the specified printing width. Cream solder printing method.