JP2007201126A - Copper concentration estimation method in fused solder, and printed board used therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a copper concentration estimation method in fused solder which is carried out simply on a production site without requiring a conventional large-scale and expensive equipment, time and effort, special knowledge, a complicated device or the like; and to provide a printed board to be used for the method. <P>SOLUTION: The copper concentration in molten solder is estimated according to the molten state of the copper pattern formed on the substrate, by bringing the copper pattern formed on the substrate into contact with the fused solder, while utilizing the relation that the rate of dissolution of solid metal is dependent on the solute concentration in fluid metal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a method for estimating a copper concentration contained in molten solder and a printed circuit board used in the method.

From the viewpoint of environmental protection, so-called lead-free solder, which excludes lead from solder used for bonding, has been applied in mounting electronic components on printed wiring boards, and Sn-Ag-Cu solder is becoming the industry standard . However, lead-free solder is more reactive with metals than conventional lead-containing solder, so dip soldering (for example, flow soldering, partial jet soldering, etc.) that brings a printed wiring board into contact with molten solder ), The problem that the through-hole copper electrode is melted to increase the copper concentration in the molten solder bath has become apparent.

An increase in the copper concentration in the molten solder causes an increase in the liquidus temperature, which adversely affects workability (particularly bridging failure). Moreover, since the hard and brittle needle-like crystal of Cu6Sn5 which is a Cu-Sn compound crystallizes out as a structure state of the solder, there is a concern about a decrease in reliability of the solder joint. On the other hand, a decrease in the copper concentration in the molten solder promotes the dissolution of the through-hole copper electrode and causes disconnection. For the above reasons, it is necessary to manage the copper concentration in the molten solder within an appropriate range.

As an elemental analysis method in molten solder, fluorescent X-ray analysis is generally used. A certain amount of solder is collected from the solder bath, cooled and solidified, processed into a desired size with a lathe, and then the weight ratio of the measurement target element is measured with a fluorescent X-ray analyzer.

Also, immersing the metal member and the probe in the molten solder, measuring the continuity between them, and using the dissolution rate, calculate the solder element concentration from the time when the metal member was dissolved in the molten solder and the continuity was lost There is a way. (For example, see Patent Document 1)

JP 2002-340884 A

However, the X-ray fluorescence analyzer can perform highly accurate analysis, but it requires labor and time to prepare a measurement sample, the device is large and expensive, and measurement requires specialized knowledge. There was a problem that it could not be easily analyzed on site. Further, the method described in Japanese Patent Application Laid-Open No. 2002-340884 can be analyzed at the production site, but has a problem that a complicated device for measuring continuity is required.

The present invention has been made to solve the above-described problems, and an object thereof is to provide a method for easily estimating the copper concentration in molten solder at a production site and a printed circuit board used in the method. It is.

The method for estimating the copper concentration in the molten solder according to the present invention estimates the copper concentration in the molten solder based on the dissolved state of the copper pattern formed on the substrate.

According to the present invention, the printed circuit board on which the copper pattern is formed is immersed in the molten solder for a certain period of time, and the copper concentration in the molten solder is estimated based on the dissolved state of the copper pattern. No need for specialized knowledge, etc. for measurement due to equipment, labor and time, or complicated equipment, eliminating the need for complicated equipment. There is an effect that the copper concentration can be estimated.

Embodiment 1 FIG.
Hereinafter, Embodiment 1 of the present invention will be described with reference to the drawings.
In the present embodiment, a method for estimating the copper concentration in the molten solder by immersing a printed board having a copper pattern formed on the substrate in the molten solder will be described as an example.
FIG. 1A shows an embodiment of a printed circuit board 7 according to the present invention. The printed circuit board 7 is formed by forming a triangular copper pattern 2 on the substrate 1. After applying a flux for removing oxide on the copper surface to the printed circuit board 7, it is immersed in a molten solder (not shown). When the printed circuit board 7 is lifted from the molten solder after a certain time, the tip of the triangular copper pattern 2 is selectively dissolved and disappears as shown in FIG. The phenomenon in which the tip portion is selectively dissolved is due to the fact that the ratio of the surface area where the molten solder contacts the volume of the copper pattern is large.
That is, the volume per unit length of the copper pattern is (height × width), whereas the surface area is (height × 2 + width), and the tip of the triangle is the volume of the copper pattern. This is because the ratio of the surface area with which the molten solder contacts is increased.

FIG. 2 is a calibration curve showing the relationship between the length of the copper pattern disappearing portion 5 and the copper concentration in the molten solder at a certain time, temperature, and jet state using the printed circuit board 7 shown in FIG. The higher the copper concentration in the molten solder, the shorter the length of the disappearance portion 5 of the copper pattern. By preparing this calibration curve in advance, the copper concentration in the molten solder can be estimated from the length of the disappearing portion 5 of the copper pattern read by the scale 3.

In the embodiment shown in FIG. 1, the triangular copper pattern 2 is formed on the substrate 1. However, the triangular copper pattern may be circular, oval, polygonal or the like. In this case, as shown in FIGS. 4 and 5, the peripheral portion or the tip portion is selectively dissolved and disappears.
Further, instead of measuring the length of the disappearance portion 5 of the copper pattern, the length of the remaining portion 4 or the remaining area of the copper pattern may be measured to estimate the copper concentration in the molten solder. In this case, it is necessary to prepare in advance a calibration curve showing the relationship between the length of the remaining portion 4 of the copper pattern to be measured and the copper concentration in the molten solder corresponding to the remaining area.

Further, in the embodiment of FIG. 1, by providing the scale 3, it is easy to measure the length of the disappearing portion 5 of the copper pattern, and thus has an effect of facilitating estimation of the copper concentration in the molten solder. When the scale 3 is not provided, there is a method of measuring using a measuring instrument such as a ruler or a caliper.

Table 1 is a table showing an example of a comparison result between the copper concentration estimation result according to the present invention and the analysis result by the fluorescent X-ray apparatus which is a precise analysis method. As shown in Table 1, the result of the estimation of the copper concentration according to the present invention, which is a simple estimation method, is very close to the analysis result by the fluorescent X-ray apparatus, which is a precise analysis method. .

Embodiment 2. FIG.
Next, a second embodiment will be described.
FIG. 3A shows a printed circuit board 7 on which a plurality of circular copper patterns 6 having different sizes are formed. When the printed circuit board 7 is immersed in the molten solder, it disappears from the small diameter pattern as shown in FIG. 3B, and disappears to the large diameter pattern as the copper concentration in the molten solder is lower. The copper concentration in the molten solder can be estimated from the number of disappearing portions 5 of the circular copper pattern or the number of remaining portions 4 of the circular copper pattern.
In this case, it is necessary to prepare in advance a calibration curve indicating the relationship between the number of disappearing portions 5 of the circular copper pattern or the copper concentration in the molten solder corresponding to the number of remaining portions 4 of the circular copper pattern. is there.

In the embodiment of FIG. 3 (a), a plurality of circular copper patterns 6 having different sizes are formed on the substrate 1. However, the circular copper pattern 6 may have other shapes such as an oval and a polygon. Good.

In the first and second embodiments, the copper concentration is estimated using the printed circuit board 7 in which the copper pattern 6 is formed on the substrate 1, but the present invention is not limited to this, and the substrate 1 Instead, a printed board in which a copper pattern 6 is formed on a material that is difficult to dissolve when immersed in molten solder, such as glass, ceramic, stainless steel, or the like, may be used.

In each of the above embodiments, the case where the printed circuit board 7 on which the copper pattern 6 is formed is immersed in the molten solder has been described. However, if the molten solder is brought into contact with the printed circuit board 7 on which the copper pattern 6 is formed, The purpose of the period is achieved.

The present invention is suitable for simply estimating the copper concentration in the molten solder at the production site, and has great industrial applicability.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram illustrating a first embodiment of the present invention, and is an explanatory diagram illustrating a triangular copper pattern shape on a printed circuit board used for estimating a copper concentration in molten solder and a copper pattern disappearance state. FIG. 2 is an example of a calibration curve showing a relationship between a copper pattern disappearance length and a copper concentration in molten solder when the triangular copper pattern of FIG. 1 is used. FIG. 9 is an explanatory diagram for explaining a second embodiment of the present invention and showing a circular copper pattern shape on a printed circuit board used for estimating a copper concentration in molten solder and a disappearance state of the copper pattern. The other example which made the shape of the triangular copper pattern in Embodiment 1 of this invention into the circular copper pattern is demonstrated, The circular copper pattern shape on the printed circuit board used for copper concentration estimation in molten solder, and its copper pattern It is explanatory drawing showing the disappearance state of. Another example in which the shape of the triangular copper pattern in the first embodiment of the present invention is a rectangular copper pattern will be described, and the rectangular copper pattern shape on the printed circuit board used for estimating the copper concentration in the molten solder and the copper pattern It is explanatory drawing showing the disappearance state of.

Explanation of symbols

1 Board
2 triangle copper pattern
3 scale
4 Remaining copper pattern
5 Loss of copper pattern
6 circular copper pattern
7 Printed circuit board

Claims (9)

A copper pattern is formed on a substrate, the copper pattern is brought into contact with molten solder, and the copper concentration in the molten solder is estimated from the amount of the copper pattern dissolved by contact with the molten solder. Method for estimating copper concentration in molten solder. 2. The method for estimating a copper concentration in molten solder according to claim 1, wherein the copper pattern has a shape in which the ratio of the surface area to the volume changes continuously. A printed circuit board comprising: a substrate; and a copper pattern formed on the substrate and brought into a molten state upon contact with molten solder. The printed circuit board according to claim 3, wherein the copper pattern has a shape in which a ratio of a surface area to a volume continuously changes. The printed circuit board according to claim 3 or 4, wherein the copper pattern has a circular shape, an oval shape, or a polygonal shape. The printed circuit board according to claim 4, wherein the copper pattern is a triangle. 4. The printed circuit board according to claim 3, wherein the copper pattern has a plurality of large and small shapes having different ratios of surface area to volume. The printed circuit board according to claim 7, wherein the copper pattern is circular. The printed circuit board according to any one of claims 3 to 8, further comprising a scale capable of reading the shape of the copper pattern.

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