JP2005069706A - Contact angle measuring method of solder paste, and contact angle measuring device of solder paste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a contact angle measuring method and its device of solder paste capable of observing not only a wetting behavior of the solder but also a wetting behavior of flux. <P>SOLUTION: This device is constituted of a sample stand cum heater 1a for placing and heating a test piece 2a on which the solder paste 4a is printed, an illumination device 5a capable of adjusting the light converging state, for illuminating the solder paste 4a and its periphery, a light receiving camera 6 loaded on a moving stage 7, for photographing the state of the solder paste 4a, a monitor television 8 for projecting the image, and an unillustrated means (for example, an image analysis means) for determining a contact angle from the image of the monitor television 8. The converging state of illumination light 51a from the illumination device 5a is adjusted, thereby discriminating an opaque solder image from a transparent or translucent flux image. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for measuring a contact angle representing a wet state of solder and flux on a substrate in order to elucidate and optimize a mechanism of a solder bonding process of an electronic device.
[0002]
[Prior art]
The contact angle of the liquid is generally measured at room temperature in a normal air atmosphere using an apparatus configured as shown in FIG.
The contact angle measuring device includes a measuring stage 1 on which a test piece 2 is placed, an illumination device 5 and a light receiving camera 6 disposed on both sides of an extended line parallel to the surface of the test piece 2, and the position of the light receiving camera 6 on the extended line. And a monitor television 8 that projects an image captured by the light receiving camera 6 and measures a contact angle from the image.
The contact angle is measured as follows.
1) Place test piece 2 on measurement stage 1,
2) A predetermined amount of the sample solution 4 is dropped on the test piece 2 using the syringe 3 from above,
3) The sample liquid 4 dropped into a teardrop shape is irradiated with illumination light 51 from one side (from the left side in FIG. 4) by the illuminating device 5, and the shadow of the sample liquid 4 is reflected by the light receiving camera 6 on the opposite side. Image
4) The shadow image is displayed on the monitor TV 8, and the contact angle is obtained from the image shape.
[0003]
Since the contact angle θ, the surface tension γ _s of the test piece 2, the surface tension γ ₁ of the sample liquid 4, and the interfacial tension γ _{sl of} the test piece 2 and the sample liquid 4 are in the relationship shown in FIG. By obtaining the contact angle θ, a physical property value such as an interfacial tension between the test piece and the sample liquid can be calculated, and an analysis such as a simulation can be performed.
However, in the case of the contact angle measuring apparatus as described above, it is impossible to measure the contact angle in the solder joining process of cream solder in which solder particles and liquid flux are mixed in a paste form. The reason for this is that the cream solder has a high viscosity (170 to 250 Pa · s), so it cannot be supplied onto the test piece using a syringe, and furthermore, it does not have a heating means. This is because the necessary heat treatment process cannot be simulated.
[0004]
As a method for observing the solder wetting behavior in the heat treatment process, there is a “method and apparatus for observing solder wetting behavior” disclosed in Patent Document 1. In this method, solder particles are placed on a test piece, how the solder spreads in the process of heat treatment is observed from the top surface, and how the contact angle changes is observed from the side surface. In the case of observing the behavior in a predetermined atmosphere, countermeasures for preventing the observation window from being contaminated by flux or solvent vapor are also shown.
[0005]
[Patent Document 1]
JP-A-5-126715 [0006]
[Problems to be solved by the invention]
According to said patent document 1, the wetting behavior of the cream solder printed on the test piece can be observed. However, in recent solder joint technology, it is necessary to develop solder joint technology using solder that is not a eutectic composition due to the trend toward lead-free, and solder particles of various compositions and fluxes of various compositions are mixed in a paste form. It has become necessary to print the cream solder on the test piece and observe the wetting behavior in the heat treatment process, particularly the contact angle. In this case, not only the solder wetting behavior but also the flux wetting behavior is important information. The reason for this is that, in the case of conventional lead-tin eutectic solder, the solder has a simple wetting behavior in which the solder melts and spreads at the eutectic point after the flux spreads wet. In the process of finding a desired solder and flux combination, the combination does not show a simple behavior like conventional lead-tin eutectic solder, and the flux wetting behavior and solder wetting behavior are different. In some cases, the behavior is completely different. Therefore, it has become necessary to observe not only the solder wetting behavior but also the flux wetting behavior.
[0007]
The heat treatment process of the cream solder printed on the test piece can be divided into four regions as shown in FIG. FIG. 7 schematically shows an example of the state of cream solder in each region, (a) is a side view showing the state of region I (initial state), and (b) is a region II (solvent transpiration) state. It is a side view which shows a state, (c) is a side view which shows the state of area | region III (flux wetting), (d) is area IV (solder melting *
It is a side view which shows the state of wetting.
Region I (initial state) is a region where the temperature is low and the printed state is maintained, and the cream solder 4a is still printed on the test piece 2a.
[0008]
Region II (solvent transpiration) is a region where the solvent 41 in the cream solder 4a evaporates as the temperature rises from the region I, but the shape hardly changes. The temperature range is 70 ° C to 150 ° C.
Region III (flux wetting) is a region where the flux 42 wets and spreads on the test piece 2a, but the solder particles 43 remain solid. It is necessary to measure the contact angle of the flux 42 indicating the wet state of the flux 42 with respect to the test piece 2a from this region. The state of FIG. 7C is close to the initial state of this region in the case of conventional cream solder of lead-tin eutectic solder.
[0009]
Region IV (solder melting / wetting) is a region in which the solder particles 43 are melted and spread on the test piece 2a in addition to the spreading of the flux 42. In addition to the measurement of the contact angle of the flux 42, It is also necessary to measure the contact angle of the molten solder 43a indicating the wet state of the molten solder 43a with respect to the test piece 2a. The state of FIG. 7D is close to the initial state of this region in the case of the conventional cream solder of lead-tin eutectic solder, and in the final stage, the flux 42 spreads much more widely and the molten solder 43a. Is much smaller than the state shown in FIG. When the eutectic solder is not used, the melting of the solder is not completed at a constant temperature, but is completed through a certain temperature range, and the composition of the molten solder 43a changes during that time. Presents.
[0010]
As is clear from the above description, in order to obtain a desired solder joint, not only the solder wetting behavior but also the flux wetting behavior is accurately grasped, and the optimum combination of solder and flux and the heat treatment conditions are determined. It is necessary to find out. An object of the present invention is to provide a cream solder contact angle measuring method and a cream solder contact angle measuring apparatus capable of observing not only the solder wetting behavior in the heat treatment process for solder bonding but also the flux wetting behavior. .
[0011]
[Means for Solving the Problems]
The invention according to claim 1 is a cream for measuring a contact angle representing a wet state of solder and flux with respect to a test piece in a heat treatment process of a test piece printed with cream solder in which solder particles and liquid flux are mixed in a paste form. A solder contact angle measurement method, in which the light condensing state of the illumination light to the cream solder is adjusted by an illumination means capable of adjusting the light condensing state, and an opaque solder image and a transparent or translucent flux image And the contact angles of solder and flux are measured.
If the cream solder, which has been heat-treated and the solder particles are melted and separated into molten solder and flux, is irradiated with concentrated high-intensity illumination light, the image of the solder is formed by the light transmitted through the transparent or translucent flux. It can be clearly understood. On the other hand, when the illumination light that is not collected so much is irradiated as a whole, the image of the flux is clearly captured. Of course, images of solder and flux may be captured at the same time, but by irradiating illumination light with the light condensing state adjusted, individual images of solder or flux can be captured more clearly.
[0012]
The invention according to claim 2 is a cream for measuring a contact angle representing a wet state of solder and flux with respect to a test piece in a heat treatment process of a test piece printed with cream solder in which solder particles and liquid flux are mixed in a paste form. A solder contact angle measuring device, a heating means for heating the test piece, a cream solder printed on the test piece and an illuminating means capable of adjusting a condensing state for illuminating the periphery thereof, and a heat treatment of the cream solder An image pickup means for picking up the state of solder and flux in the process, a monitor television for displaying an image picked up by the image pickup means, and a contact angle measuring means for obtaining a contact angle from the image of the monitor television are provided.
As described in the invention of claim 1, since the light-collecting state-adjustable illumination means is provided, in the process of heat-treating the cream solder printed on the test piece, individual images of the solder or the flux become clearer. Can be caught.
[0013]
The invention of claim 3 is the invention of claim 2, wherein the heating means incorporates a pulse heater in a heating stage made of a material having a small linear expansion coefficient and high heat resistance.
By using a heating means incorporating a pulse heater, the temperature of the test piece can be raised sufficiently rapidly, so that the heating temperature profile of the actual soldering process can be simulated, and step heating can be used for each step. The wet state of solder and flux can be observed.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The solder solder contact angle measuring method and cream solder contact angle measuring device according to the present invention can adjust the light condensing state in order to grasp the wetting behavior of the cream solder printed on the test piece during the heat treatment process. By adjusting the condensing state of the illumination means, the wet state of the flux and the molten solder on the test piece is clearly imaged, and the contact angles of the flux and the molten solder can be reliably measured. In addition, a pulse heater is incorporated in the heating means so that the heat treatment process of the solder joining process can be simulated.
In the following, embodiments of the present invention will be described in more detail using examples.
In addition, the same code | symbol is attached | subjected to the part of the same function as a prior art.
[0015]
FIG. 1 is a block diagram showing an embodiment of a cream solder contact angle measuring device according to the present invention. FIG. 2 shows the shape of cream solder in a molten state for explaining the function of the embodiment. ) Is a side view of the entire cream solder in a molten state, (b) is a side view of only the molten solder, and (c) is a side view of only the flux.
In the case of this embodiment, a sample to be measured is obtained by printing the cream solder 4a on the test piece 2a using a metal mask made of stainless steel or the like. This sample is placed on a sample stage / heater 1a which also serves as a measurement stage and a heater. On a plane parallel to the surface of the sample table / heater 1a, an illumination device 5a and a light receiving camera 6 are arranged on both sides of the sample table / heater 1a. The illuminating device 5a has a function of adjusting the condensing state, and irradiates the cream solder 4a and its periphery with illumination light 51a in a desired condensing state. A halogen lamp or the like is used as the light source of the illumination device 5a. The light receiving camera 6 is mounted on the moving stage 7, and the position of the light receiving camera 6 is adjusted on a plane parallel to the surface of the sample stage / heater 1a in order to clearly capture an image of a desired position of the cream solder 4a. The image captured by the light receiving camera 6 is displayed on the monitor television 8 and is captured by image analysis means including a video, an image capturing device, etc. (not shown), and the contact angle is obtained by the image analysis means.
[0016]
The sample stage / heater 1a is a heat source capable of raising the temperature by about 50 ° C. per second in a measurement stage made of a material having a small coefficient of linear expansion and high heat resistance such as stainless steel or Inconel. For example, a pulse heater using a ceramic collet is incorporated. The reason why the measurement stage is made of a material having a small linear expansion coefficient is to reduce the thermal deformation of the measurement stage and stabilize the heat conduction to the test piece 2a. The reason why a heat source with a high temperature increase rate is used is to measure the contact angle in a state close to the heating temperature profile of the actual solder bonding process by performing step heating.
The cream solder 4a in which the solder particles are melted is divided into a transparent or yellow translucent flux 42 and an opaque molten solder 43a. For example, as shown in FIG. Covered. However, in the image captured by the light receiving camera 6, the flux 42 and the molten solder 43a are not clearly separated in this way, and it is difficult to accurately measure the contact angles of each. This difficulty is due to the fact that the flux 42 is transparent or yellow translucent, making it difficult to photograph the shape clearly, and that the flux 42 covers the portion for measuring the contact angle of the molten solder 43a. Therefore, it is necessary to separately capture the respective images by changing the condensing state of the illumination light 51a between the case of measuring the contact angle of the flux 42 and the case of measuring the contact angle of the molten solder 43a. . For example, in the case of irradiating a small amount of illumination light 51a that is not so concentrated, only the outer shape of the flux 42 is projected, and the shape of the internal molten solder 43a becomes unclear. When an image of the state is obtained and irradiated with the concentrated high-intensity illumination light 51a, the shape of the internal molten solder 43a appears clearly by the light transmitted through the flux 42, and the image in the state of FIG. Is obtained.
[0017]
In the above embodiments, no special atmosphere control is performed, but by combining with an atmosphere control box or the like, it is possible to measure a contact angle in an inert gas atmosphere such as a nitrogen atmosphere. 3A and 3B show an example of the atmosphere control unit, in which FIG. 3A is an overall configuration diagram including a front view of the atmosphere control box, and FIG. 3B is a plan sectional view of the atmosphere control box.
The atmosphere control unit 9 includes an atmosphere control box 91 containing a heater embedded base plate 911 (corresponding to the sample table / heater 1a in FIG. 1) for heat-treating the test piece 2a printed with the cream solder 4a, and an inert gas. It comprises a pump 92 for circulation, a water tank 93 for removing flux vapor in the circulating inert gas, and a nitrogen supply part 94 for supplying nitrogen as an inert gas.
[0018]
The atmosphere control box 91 has two air supply ports 912 that supply inert gas to both sides of the lower right side, an exhaust port 913 that discharges inert gas to the upper right center, a cooling plate 914 on the upper surface, and both front and rear surfaces. Glass windows 915 and 916 for illumination light irradiation and observation / imaging, and a plurality of air outlets 917 for injecting an inert gas supplied from the air inlet 912 to the front and rear sides of the lower part inside the atmosphere control box 91. And a door for taking in and out the sample (not shown) on the left side.
When the contact angle is measured using such an atmosphere control box 91, the vapor cannot be measured if vapor such as flux condenses on the glass windows 915 and 916 and cloudes them, so that the gas is supplied from the air supply port 912. This is prevented by ejecting the inert gas from the air outlet 917. The inert gas ejected from the fumarole 917 carries vapor such as flux evaporated from the cream solder 4a to the upper part and condenses most of it on the cooling plate 914. The remaining inert gas containing steam such as flux is exhausted from the exhaust port 913 by the pump 92, the remaining steam in the water tank 93 is completely removed, and is supplied to the atmosphere control box 91 from the air supply port 912 again. The
[0019]
When the atmosphere control box 91 is rotated 90 degrees clockwise and replaced with the position of the sample table / heater 1a in FIG. 1, the contact angle in the atmosphere controlled state can be measured.
[0020]
【The invention's effect】
In the first aspect of the invention, the light collecting state of the illuminating light to the cream solder is adjusted by the illumination means capable of adjusting the light collecting state, and an opaque solder image and a transparent or translucent flux image are obtained. Separate and measure each contact angle of solder and flux. If the cream solder, which has been heat-treated and the solder particles are melted and separated into molten solder and flux, is irradiated with concentrated high-intensity illumination light, the image of the solder is formed by the light transmitted through the transparent or translucent flux. It can be clearly understood. On the other hand, when the illumination light that is not collected so much is irradiated as a whole, the image of the flux is clearly captured. Of course, images of solder and flux may be captured at the same time, but by irradiating illumination light with the light condensing state adjusted, individual images of solder or flux can be captured more clearly. Therefore, according to the present invention, it is possible to provide a method for measuring the contact angle of cream solder that can observe not only the solder wetting behavior but also the flux wetting behavior.
[0021]
According to the second aspect of the present invention, since the illumination means capable of adjusting the light condensing state is provided, as described in the first aspect of the invention, in the process of heat-treating the cream solder printed on the test piece, Individual images of flux can be captured more clearly. Therefore, according to the present invention, it is possible to provide a cream solder contact angle measuring device capable of observing the flux wetting behavior in addition to the solder wetting behavior.
The invention of claim 3 is the invention of claim 2, wherein the heating means incorporates a pulse heater in a heating stage made of a material having a small linear expansion coefficient and high heat resistance. By using a heating means incorporating a pulse heater, the temperature of the test piece can be raised sufficiently rapidly, so that the heating temperature profile of the actual soldering process can be simulated, and step heating can be used for each step. The wet state of solder and flux can be observed.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a cream solder contact angle measuring apparatus according to the present invention. FIG. 2 shows the shape of cream solder in a molten state for explaining the function of the embodiment. (B) is a side view of only the molten solder, (c) is a side view of only the flux [FIG. 3] shows an example of the atmosphere control unit, and (a) is a view of the atmosphere control box. Overall configuration including front view, (b) is a cross-sectional plan view of the atmosphere control box. FIG. 4 is a configuration diagram showing an example of a liquid contact angle measuring device according to the prior art. 6 is a diagram for explaining the state of the cream solder in the heat treatment process. FIG. 7 schematically shows the state of the cream solder for each region in FIG. 6, (a) is a side view showing the state of region I; b) is a side view showing the state of region II, and (c) is the region. Side view showing a state of II, (d) a side view showing a state of the region IV is [EXPLANATION OF SYMBOLS]
DESCRIPTION OF SYMBOLS 1 Measurement stage 1a Sample stand and heater 2, 2a Test piece 3 Syringe 4 Sample liquid 4a Cream solder 41 Solvent 42 Flux 43 Solder particle 43a Molten solder 5, 5a Illuminating device 51, 51a Illuminating light 6 Light receiving camera 7 Moving stage 8 Monitor television DESCRIPTION OF SYMBOLS 9 Atmosphere control part 91 Heat processing tank 911 Heater embedding baseplate 912 Air supply port 913 Exhaust port 914 Cooling plate 915 Glass window 916 Fume port 92 Pump 93 Water tank 94 Nitrogen supply part

Claims (3)

A solder solder contact angle measurement method for measuring a contact angle representing a wet state of solder and flux on a test piece in a heat treatment process of a test piece printed with cream solder in which solder particles and liquid flux are mixed in a paste form. There,
By adjusting the condensing state of the illuminating light to the cream solder by the illumination means capable of adjusting the condensing state, the opaque solder image and the transparent or translucent flux image are separated, and each of the solder and the flux A contact angle measurement method for cream solder, characterized in that the contact angle of the solder is measured. A contact angle measuring device for cream solder for measuring a contact angle representing a wet state of solder and flux on a test piece in a heat treatment process of a test piece printed with solder paste and solder paste mixed in a paste form. There,
Heating means for heating the test piece;
A light-adjustable illumination means for illuminating the cream solder printed on the test piece and its surroundings;
Imaging means for imaging the state of solder and flux in the heat treatment process of cream solder;
A monitor television for displaying an image captured by the imaging means;
Contact angle measuring means for obtaining a contact angle from an image on a monitor television;
An apparatus for measuring the contact angle of cream solder, comprising: 3. The contact angle measuring device for cream solder according to claim 2, wherein the heating means includes a pulse heater incorporated in a heating stage made of a material having a small linear expansion coefficient and high heat resistance.

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