JP6191051B2 - X-ray fluorescence analyzer - Google Patents

Description

  The present invention relates to an X-ray fluorescence analyzer for analyzing the composition of Sn-Ag solder bumps.

  Conventionally, a lead-free Sn-Ag solder bump formed on a semiconductor substrate has been used as an electrode of a semiconductor device (see Patent Document 1). However, in order to maintain and improve the yield of the semiconductor device, It is necessary to manage the composition of the Sn-Ag solder bumps formed above. In the management of this composition, it is also required that the solder bumps are less segregated, that is, the difference between the overall composition of the solder bumps and the composition of the surface of the solder bumps is within an allowable range.

  In this connection, the Sn-Pb lead solder used in the printed board unit on which the electronic component is mounted was obtained by taking the difference between the Sn-Kα ray distribution and the Sn-Lα ray distribution. When the distribution of Sn and the distribution of Pb overlap, there is a first prior art that determines that the Sn—Pb alloy, that is, lead solder, is present not inside the surface of the electronic component mounted on the printed board unit (See Patent Document 2). In the first prior art, the distribution of Sn—Pb (high melting point solder) inside the electronic component and the distribution of Sn—Pb (electrode plating or mounting solder) on the surface of the electronic component are displayed.

  Further, in a consumer product such as a toy, a process for determining whether lead is on the surface of the product or inside based on the ratio of the measured intensity of the Pb-Lα ray and the measured intensity of the Pb-Lβ ray. There is also a prior art 2 (see Patent Document 3).

Japanese Patent No. 4425799 JP 2007-163183 A US Pat. No. 8,155,268

  However, even if the first conventional technique is applied to a substrate on which Sn-Ag solder bumps are formed, the distribution of Sn-Ag solder bumps formed on the substrate is distributed as Sn-Ag alloy distribution on the substrate surface. It is not possible to determine whether or not the difference between the overall composition of the solder bumps and the composition of the surface of the solder bumps is within an allowable range. Further, even if the second conventional technique is applied to a substrate on which Sn-Ag solder bumps are formed, it is only confirmed that Sn or Ag is present on the surface of the substrate, and the overall composition of the solder bumps It cannot be determined whether or not the difference from the composition of the surface of the solder bump is within an allowable range.

  Therefore, the present invention provides an X-ray fluorescence analyzer capable of determining whether or not the difference between the overall composition and the surface composition is within an allowable range for Sn-Ag solder bumps formed on a substrate. For the purpose.

  In order to achieve the above object, the present invention provides a means for detecting the intensity of fluorescent X-rays generated by irradiating a primary X-ray from a X-ray source onto a sample in which a Sn-Ag solder bump is formed on a substrate. X-ray fluorescence analysis apparatus for measuring with a quantification means and segregation evaluation means. Based on the ratio of the intensity of Ag-Kα rays and the intensity of Sn-Kα rays measured by the detecting means, the quantitative means is the concentration of silver in the entire solder bump (the entire surface including not only the surface but also the inside). And the surface concentration, which is the silver concentration on the surface of the solder bump, is obtained based on the ratio of the intensity of the Ag-Lα ray and the intensity of the Sn-Lα ray measured by the detecting means. The segregation evaluation means evaluates segregation in the solder bumps depending on whether or not the difference between the total concentration and the surface concentration is a predetermined value or less.

  The density at which the solder bumps are arranged on the substrate varies depending on the sample. If the density of the solder bumps is high even if the overall concentration is the same, the measurement intensity of the Ag-Kα line increases. Therefore, when determining the total concentration, it is not possible to accurately determine the total concentration based on the measured intensity of the Ag-Kα ray itself. According to the present invention, first, when determining the total concentration by the quantitative means, it is not based on the measured intensity of the Ag-Kα ray itself but based on the ratio of the measured intensity of Sn-Kα ray from tin coexisting with silver. . Therefore, it is possible to accurately obtain the total concentration without being affected by the density of solder bumps on the substrate that differs depending on the sample. The reason why the Kα line is used is that the Kα line is generated not only from the surface of the solder bump but also from the whole.

  Similarly, when determining the surface concentration which is the concentration of silver on the surface of the solder bump by the quantitative means, it is not based on the measured intensity of the Ag-Lα ray but based on the ratio to the measured intensity of the Sn-Lα ray. The surface concentration can be obtained accurately. The reason why the Lα line is used is that the Lα line is generated only from the surface of the solder bump (strictly, near the surface). And the segregation evaluation means evaluates the segregation in the solder bumps depending on whether or not the difference between the total concentration and the surface concentration obtained accurately is a predetermined value or less, so that the Sn-Ag system formed on the substrate It can be determined whether or not the difference between the overall composition and the surface composition is within an allowable range.

1 is a schematic view showing a fluorescent X-ray analyzer according to an embodiment of the present invention. It is the elements on larger scale of the sample of FIG.

  Hereinafter, an X-ray fluorescence analyzer according to an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, this apparatus irradiates a sample 3 placed on a sample stage 8 with primary X-rays 2 from an X-ray source 1 such as an X-ray tube, and generates an intensity of fluorescent X-rays 4 generated. Is a fluorescent X-ray analysis apparatus that measures the amount of light by a detection means 9, and includes a quantitative means 10 and a segregation evaluation means 11. Specifically, the quantification means 10 and the segregation evaluation means 11 are configured by a computer and input / output devices connected thereto.

  The detection means 9 includes a spectroscopic element 5 that separates fluorescent X-rays 4 generated from the sample 3 and a detector 7 that measures the intensity of each spectroscopic fluorescent X-ray 6. The detection means 9 using the spectroscopic element 5 includes a fixed type in which the wavelength of the fluorescent X-ray 4 to be measured is fixed and a scanning type in which the wavelength of the fluorescent X-ray 4 to be measured can be scanned. Any number may be provided. In addition, a detector having high energy resolution can be used as the detection means without using the spectroscopic element 5.

  As shown in the partial enlarged view of FIG. 2, the sample 3 to be analyzed is composed of a substrate 3a and a number of Sn-Ag solder bumps 3b formed thereon. A large number of solder bumps 3b are arranged in the left-right direction and the depth direction on the paper surface of FIG. The density at which the solder bumps 3b are arranged on the substrate 3a (the number of solder bumps 3b per unit area of the substrate 3a) varies depending on the sample 3.

  First, the quantification means 10 of FIG. 1 is based on the ratio of the intensity of Ag-Kα rays and the intensity of Sn-Kα rays measured by the detection means 9 by a known calibration curve method, that is, using a standard sample in advance. By applying the prepared calibration curve, an overall concentration Ct (%) which is the concentration of silver in the entire solder bump 3b (the entire surface including not only the surface of the solder bump 3b but also the inside) is obtained.

  Here, the reason why the Kα line is used is that the Kα line is generated not only from the surface of the solder bump 3b but also from the whole. The reason why the measurement intensity of Ag-Kα ray is based on the ratio of the measurement intensity of Sn-Kα ray is as follows. Even if the total concentration Ct is the same, if the density of the solder bumps 3b is high, the measured intensity of the Ag-Kα line increases. Therefore, when determining the total concentration Ct, it is not possible to accurately determine the total concentration Ct based on the measured intensity of the Ag-Kα ray itself. Therefore, it was not based on the measured intensity of the Ag-Kα ray itself but based on the ratio with the measured intensity of the Sn—Kα ray from tin coexisting with silver. As a result, the total concentration Ct can be accurately obtained without being affected by the density of the solder bumps 3b.

  Further, the quantification means 10 is based on the ratio of the intensity of Ag-Lα ray and the intensity of Sn-Lα ray measured by the detection means 9, the silver concentration on the surface of the solder bump 3 b by the well-known calibration curve method. The surface concentration Cs (%) is obtained. Here, the reason why the Lα ray is used is that the Lα ray is generated only from the surface of the solder bump 3b (strictly, near the surface). In determining the surface concentration Cs, the surface concentration Cs can be accurately determined because it is not based on the measured intensity of the Ag-Lα ray but based on the ratio to the measured intensity of the Sn-Lα ray.

  Then, the segregation evaluation means 11 determines whether or not the difference between the total concentration Ct and the surface concentration Cs (a value obtained by subtracting the smaller value from the larger value), that is, | Ct−Cs | The segregation in the solder bump 3b is evaluated. For example, when the predetermined value is 0.1, when | Ct−Cs | ≦ 0.1, it is evaluated that the degree of segregation in the solder bump 3b is within an allowable range, and | Ct−Cs |> 0.1. In this case, it is evaluated that the degree of segregation in the solder bump 3b exceeds the allowable range. The result of the evaluation is displayed on a liquid crystal display (not shown), for example.

  Note that the total concentration Ct and the surface concentration Cs are values for a region of the sample 3 that is irradiated with the primary X-ray 2 and that the detection means 9 expects. It moves with respect to the source 1 and the detection means 9, and repeats the operation of the measurement, quantification means 10 and segregation evaluation means 11 by the detection means 9 described above.

  As described above, according to the apparatus of the present embodiment, the total concentration Ct and the surface concentration Cs are accurately obtained, and depending on whether or not the difference | Ct−Cs | Since the evaluation of segregation is performed, it is possible to determine whether or not the difference between the overall composition and the surface composition of the Sn-Ag solder bump 3b formed on the substrate 3a is within an allowable range.

  It should be noted that the determination as to whether or not the total concentration Ct and / or the surface concentration Cs is within a predetermined allowable range may be performed together, and only when the determination is within the allowable range, the overall composition and the surface concentration It may be determined whether the difference from the composition is within an acceptable range.

1 X-ray source 2 Primary X-ray 3 Sample 3a Substrate 3b Solder bump 4 Fluorescent X-ray 9 Detection means 10 Quantification means 11 Segregation evaluation means

Claims (1)

A fluorescent X-ray analyzer that irradiates a sample, on which a Sn-Ag solder bump is formed on a substrate, with a primary X-ray from an X-ray source and measures the intensity of the generated fluorescent X-rays with a detection means,
Based on the ratio of the intensity of the Ag-Kα ray measured by the detecting means and the intensity of the Sn-Kα ray, the total concentration, which is the silver concentration in the entire solder bump, is obtained, and the Ag− measured by the detecting means. Quantitative means for determining the surface concentration, which is the concentration of silver on the surface of the solder bump, based on the ratio between the intensity of the Lα ray and the intensity of the Sn-Lα ray;
A fluorescent X-ray analysis apparatus comprising segregation evaluation means for evaluating segregation as a difference in composition between the whole and the surface of a solder bump depending on whether or not a difference between the total concentration and the surface concentration is a predetermined value or less.

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