JP2016006213A - Etching method and etching device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an etching method which can shorten the time required for etching a solder matrix and an etching device using the same.SOLUTION: A solder joint 4 is immersed in etchant 7 and the etchant 7 in which the solder joint 4 is immersed then has ultrasound applied thereto until a solder matrix 5 is etched.

Description

  The present invention relates to a method for etching a solder joint portion of an electronic component and an etching apparatus using the same.

  In evaluating the soldering state of an electronic component, a particularly important analysis point is the “joining interface” between the underlying land and the solder. Conventionally, a cross-sectional analysis using an electron microscope has been generally used as the analysis method. However, this analysis method cannot determine the crystal grain size of the solder joint interface structure. The fineness of the structure determined from the crystal grain size is an important indicator for solder joint strength.

Non-Patent Document 1 discloses a method for analyzing the solder joint interface described above. In this method, the surface information of the solder joint interface is obtained by removing the solder matrix (solder bulk) by chemical etching. For example, the solder matrix at the solder joint is dissolved by immersing the solder joint of the electronic component in an etching solution.
Note that, in the analysis method of Non-Patent Document 1, the purpose is to observe the crystal state of the solder joint interface structure. Therefore, the etching of the solder matrix must be performed so as not to affect the crystal state.

Yoshikawa Shunsaku, Tachibana Ken, Yamanaka Yoshie, “Semiconductor Package Solder Joint Interface Analysis Technology and New Material Development Trends”, Nikka Engineering Co., Ltd. 42nd Symposium on Reliability and Maintenance, July 2012, p. 69-72

Conventionally, in order to dissolve the solder matrix without affecting the crystalline state of the solder joint interface structure, the solder matrix is gradually removed by holding the solder joint of the electronic component in an etching solution for a long time. It was. For this reason, there existed a subject that it took a long time until the solder joint interface was exposed to the state which can be analyzed.
For example, depending on the amount of solder in the solder joint, the composition of the etching solution, and the holding environment, it takes about 24 hours until the solder joint interface is exposed to an analyzable state. This is a significantly longer time than the time required to obtain a sample to be analyzed by another analysis method.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an etching method and an etching apparatus using the same that can shorten the time required for etching the solder matrix.

  An etching method according to the present invention is an etching method for etching a solder matrix of a solder joint portion, the step of immersing the solder joint portion in an etching solution, and the solder matrix with respect to the etching solution in which the solder joint portion is immersed. Applying an ultrasonic wave until the material is etched.

  According to the present invention, it is possible to shorten the time required for etching the solder matrix without affecting the crystal state of the solder joint interface structure.

It is a figure which shows the outline | summary of the solder joint part of an electronic component. It is a figure which shows the etching method which concerns on Embodiment 1 of this invention. It is a SEM image which shows the state of the solder joint part in an etching process.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a solder joint portion of an electronic component. FIG. 1A shows an example of an electronic component 1 mounted on a substrate 2 by soldering. The lead terminal 3 of the electronic component 1 is soldered after being inserted into a through hole formed in the substrate 2. Thereby, the solder joint part 4 is formed. Although the structure of FIG. 1A is shown as an example of the electronic component 1, the present invention is not limited to this and can be applied to a surface mount component.

  FIG. 1B is an enlarged view of the portion denoted by reference symbol A in FIG. As shown in FIG. 1B, a solder joint interface 6 is formed between the solder matrix 5 and the base land 2a (shaded portion) of the substrate 2. The solder matrix 5 is a solder portion where the lead terminals 3 of the electronic component 1 and the substrate 2 are soldered.

When observing crystal grains of the solder joint interface 6 by the analysis method of Non-Patent Document 1, it is necessary to remove the solder matrix 5. Therefore, in the present invention, an etching solution 7 prepared for etching the solder matrix 5 is used.
First, as shown in FIG. 2A, an etching solution 7 is injected into a container 8 in which the solder joints 4 are arranged. Here, a sufficient amount of etching solution 7 is used so that the solder matrix 5 is completely immersed. As a result, the liquid level of the etching solution 7 becomes higher than the uppermost portion (vertex) of the solder matrix 5. In addition, although the board | substrate 2 with which the electronic component 1 was mounted via the solder junction part 4 is arrange | positioned in the actual container 8, only the solder junction part 4 is arrange | positioned in the container 8 in FIG. It is described as being.

  Next, the said container 8 is arrange | positioned to the ultrasonic tank of the ultrasonic generator 9, as shown in FIG.2 (b). The ultrasonic tank is filled with an ultrasonic transmission medium 10 such as water, and the ultrasonic waves generated by the ultrasonic generator 9 are transmitted via the ultrasonic transmission medium 10 to the etching solution 7 and the solder joint 4 of the container 8. Is transmitted to. The etching degree of the solder matrix 5 may be appropriately confirmed by an operator visually.

As shown in FIG. 2C, when the solder matrix 5 is completely etched and the solder joint interface 6 is exposed, the application of ultrasonic waves is stopped, and the substrate 2 with the solder joint interface 6 exposed is taken out from the container 8. Processing is complete.
The applied ultrasonic wave is an inaudible (> 20 kHz) sound wave (coherent wave) having a large frequency, and a high energy density is obtained at a short wavelength. This ultrasonic vibration promotes a chemical reaction in which the solder matrix 5 is etched.

  The ultrasonic waves applied as described above are transmitted to the solder matrix 5 through the etching solution 7. Therefore, when the liquid level of the etching solution 7 is lower than the top of the solder matrix 5 in the container 8, a part of the solder matrix 5 does not come into contact with the etching solution 7 and the ultrasonic wave does not reach, The effect of promoting etching cannot be obtained.

  Moreover, although there is no restriction | limiting about the size of the container 8, if the size of the container 8 is too large with respect to the board | substrate 2 with which the electronic component 1 was mounted via the solder junction part 4, when an ultrasonic wave is applied, The substrate 2 may move and turn over. If the substrate 2 is turned upside down in the container 8, it may be difficult to check the state of etching, or the exposed solder joint interface 6 may collide with the inner wall of the container 8 and be damaged. Therefore, it is preferable to use a container 8 having such a size that the substrate 2 does not move. However, the size of the container 8 is not limited as long as the substrate 2 has a structure or mechanism that does not turn over.

  If the amount of the ultrasonic transmission medium 10 such as water is too large, the container 8 containing the etching solution 7 may be lifted by buoyancy and fall down in the ultrasonic bath. For this reason, it adjusts so that the container 8 may not fall down.

In the present invention, etching is remarkably promoted by applying ultrasonic waves.
For example, when the etching solution 7 having the same composition is used for the solder joint portion 4 having the same solder amount and composition and no ultrasonic wave is applied, it takes about 24 hours until the solder matrix 5 is completely etched. In short, the experimental result shortened to about 1 hour by applying ultrasonic waves has been obtained.

  FIG. 3 is an SEM (scanning electron microscope) image showing the state of the solder joint in the etching process. FIGS. 3A to 3E are SEM images of the solder matrix 5 viewed from the B direction in FIG. 1B. Further, the flow of S0 (prior art) is a case where etching is performed without applying ultrasonic waves, and the flow of S1 (the present invention) is a case where etching is performed by applying ultrasonic waves. In addition, the etching liquid 7 of the same composition is used for S0 and S1 in the solder joint part 4 of the same solder amount and composition.

  FIG. 3A is an SEM image in an initial state where the substrate 2 including the solder joint portion 4 is placed in the container 8 and the etching solution 7 is injected. At this stage, there is no difference between S0 and S1, and the solder matrix 5 is not etched. In the flow of S <b> 0, the process only waits in a state where the substrate 2 is immersed in the etching solution 7 in the container 8.

  The SEM image in FIG. 3B in the flow of S1 shows the state of the solder matrix 5 immediately after the container 8 is placed in an ultrasonic bath and application of ultrasonic waves is started. At this stage, the etching has not yet progressed, and the state is the same as in FIG.

Thereafter, when about 1 hour has elapsed since the start of application of ultrasonic waves, as shown in FIG. 3C, the solder matrix 5 is completely etched, and the crystal grains 5a of the solder joint interface 6 are exposed. It has become. Note that FIG. 3C schematically shows the shape of the crystal grains.
Even in the case where etching is promoted by applying ultrasonic waves in this way, it is possible to obtain the solder joint interface 6 in a surface state (crystal state) capable of accurately measuring the crystal grain size.

On the other hand, when no ultrasonic wave is applied, the SEM image at the same time is as shown in FIG. In this case, the etching is not progressing, and the crystal grain 5b shown by the broken line is not visible.
FIG. 3E is an SEM image when about 24 hours have elapsed without applying ultrasonic waves after the etching is started. When no ultrasonic wave is applied in this way, it takes about 24 hours to obtain the solder joint interface 6 where the crystal grains 5b are exposed.
The time for completing the etching varies depending on conditions such as the solder amount and solder composition of the solder joint portion 4 and the composition of the etching solution 7. However, in any case, the etching time is shortened by applying the ultrasonic wave as compared with the case where the ultrasonic wave is not applied.

Conventionally, the solder matrix 5 is etched under as static a condition as possible so as not to damage the surface state of the solder joint interface 6. For this reason, etching took a long time and the efficiency was very poor.
On the other hand, as a result of experimental research by the inventors of the present invention, even when etching is performed by applying an ultrasonic wave, a solder having a surface state (crystalline state) similar to that obtained when etching is performed under static conditions. It was found that the bonding interface 6 was obtained. As a result, the etching time can be remarkably shortened as compared with the prior art, and the soldered state can be evaluated efficiently.
Moreover, since many samples are obtained by shortening the etching time, the reliability of the analysis of the solder joint interface 6 can also be improved.

  As described above, according to the first embodiment, the solder joint portion 4 is immersed in the etching solution 7, and the etching solution 7 in which the solder joint portion 4 is immersed is more than etched until the solder matrix 5 is etched. Apply sound waves. By doing in this way, the time required for the etching of the solder matrix 5 can be shortened without affecting the crystal state of the solder joint interface structure.

  Further, according to the first embodiment, the solder joint portion 4 is immersed in the etching solution 7 until it completely sinks. By doing in this way, the etching promotion effect by applying an ultrasonic wave is acquired.

  In the present invention, any component of the embodiment can be modified or any component of the embodiment can be omitted within the scope of the invention.

  DESCRIPTION OF SYMBOLS 1 Electronic component, 2 Board | substrate, 2a Ground land, 3 Lead terminal, 4 Solder joint part, 5 Solder matrix, 5a, 5b Joint interface structure crystal grain, 6 Solder joint interface, 7 Etching liquid, 8 Container, 9 Ultrasonic wave generation 10 Ultrasonic transmission medium.

Claims (3)

An etching method for etching a solder matrix of a solder joint,
Immersing the solder joint in an etchant;
Applying an ultrasonic wave to the etching solution in which the solder joint is immersed until the solder matrix is etched.   The etching method according to claim 1, wherein the solder joint is immersed in the etching solution until it completely sinks.   An etching apparatus using the etching method according to claim 1.

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