JP2010151760A - Method for evaluation of reliability of electronic component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for evaluation of reliability of electronic components, capable of shortly and inexpensively evaluating a status of a surface oxide film of whiskers which may result in an electric short circuit caused by a fall. <P>SOLUTION: The method includes the steps of installing the whiskers produced on a member plated including tin between a pair of electrodes so as to contact at least one of the electrodes, and applying a voltage to between the electrodes to check for a current running between the electrodes. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for evaluating the reliability of an electronic component, for example, for evaluating a decrease in reliability caused by whiskers generated in an electronic component having a plated terminal containing tin (Sn) or the like. Concerning configuration.

  In recent years, various electric and electronic devices have been developed as environmentally conscious technologies that comply with the RoHS (Restriction of Hazardous Sub- stances) directive and exclude six components such as Pb, which is a regulated component. In addition, Sn plating or the like is also used in an electrical contact portion such as a lead terminal or a connector of an LSI (Large Scale Semiconductor Integrated Circuit Device) installed in an electric / electronic device in order to cope with Pb-free.

  Among these, it is known that Sn whiskers are generated from the surface of the Sn plating film due to compressive stress applied to the plating film and defects in the oxide film on the plating surface. In particular, in a fitting part of a connector part used in an information processing device such as a personal computer, external stress is easily applied during fitting, and this external stress is considered as one type of compressive stress.

  Further, it is considered that, due to this external stress load (friction or the like), the oxide film on the plating surface is scraped off at the fitting portion and the plating film is exposed to the surface, so that whiskers are likely to occur.

  Due to the generation and growth of such whiskers, the electrical reliability of electronic devices may be deteriorated. As a direct effect, there may be a short circuit between the electrodes where the whisker occurs. As an indirect effect, the whisker drops in the electronic device due to the impact or vibration applied to the electronic device and contacts between the electrodes. If you want to.

  In order to avoid this direct influence, for example, after the whisker is grown in a temperature cycle, the length is measured without taking out the whisker, and if it is long, the electronic component is not used. (For example, refer to Patent Document 1). Alternatively, it has also been proposed to measure the whisker resistance when the whisker has grown to a predetermined length, and to warn of the risk of a short circuit when the whisker exceeds a predetermined value (see, for example, Patent Document 2).

  On the other hand, when a whisker is dropped on a wiring in an electronic device and a continuity test is performed in order to investigate an indirect influence, there are cases where the whisker is short-circuited or not even if the whisker is on the wiring. From the viewpoint of electrical reliability, only a short circuit is a problem.

As a cause of the short circuit, there is a natural oxide film on the surface of the Sn whisker similarly to the Sn plating film, and this is considered to be a partial defect of the surface oxide film. Therefore, if the state of the surface oxide film of the whisker is examined, it becomes possible to investigate the electrical reliability due to the whisker dropping.
JP 2005-101019 A JP 2001-228107 A

  However, since the thickness of the whisker is about several μmφ, the surface oxide film is a thin film having a thickness of about several nm. Therefore, in order to investigate the state of the surface oxide film, observation with an electron microscope such as a TEM (transmission electron microscope) is required.

  The length of whiskers varies from several tens to several hundreds of μm. To observe the state of the surface oxide film of one whisker with a TEM, pretreatment for observation and high magnification of the microscope are required. There is a problem that it is necessary and takes time and cost.

  In addition, in the method of avoiding the direct influence mentioned above, there exists a problem that the electrical reliability investigation by the fall of a whisker cannot be performed. In particular, in the case of Patent Document 2, it is impossible to grasp the state of the surface oxide film that causes any short circuit.

  Accordingly, an object of the present invention is to evaluate the state of the surface oxide film of the whisker that causes an electrical short circuit due to dropping in a short time and at a low cost.

  From one aspect of the present invention, an installation step of installing a whisker generated in a member plated with tin between electrodes so as to be in contact with at least one electrode of a pair of electrodes, and applying a voltage between the electrodes Thus, there is provided an electronic component reliability evaluation method including an inspection step of inspecting the presence or absence of a current flowing between the electrodes.

  According to the reliability evaluation method of the disclosed electronic component, it is only necessary to take out whisker generated in a member plated with tin and place it between the electrodes of a pair of electrodes to measure the presence or absence of current. It is possible to evaluate the reliability of electronic components in a short time and at a low cost.

  Here, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a configuration explanatory diagram of a whisker test apparatus according to an embodiment of the present invention. The whisker test apparatus comprises a whisker installation jig 10, a DC power source 21, a resistor 22, an ammeter 23, and lead wires and connection terminals for interconnecting them. In this case, the maximum voltage of the DC power supply 21 is set to 20 V or less. This is because if the voltage is too high, the sample whisker may be attracted by electrostatic attraction and move from the installation location.

  The resistor 22 may be a fixed resistor or a variable resistor. In the case of a variable resistor, for example, a range of 0.5 kΩ to 110 kΩ is set in consideration of a state when a current flows through the whisker. Also, in the case of a fixed resistor, for example, it may be set in any of the range of 0.2 kΩ to 110 kΩ, but it is set to 1 kΩ, for example, in consideration of the value of the current to be measured.

FIG. 2 is a conceptual configuration diagram of the whisker installation jig 10, and FIG. 2A is a diagram in which a pair of parallel linear electrodes 12 ₁ and 12 ₂ are provided on the insulating substrate 11. In this case, the electrodes 12 ₁ and 12 ₂ are made of, for example, Au that does not need to consider the oxide film on the surface, and a mechanism for changing the distance between the electrodes 12 ₁ and 12 ₂ is provided, or electrodes having different distances A plurality of pairs are provided. Also, FIG. 2 (b) is obtained by providing a pair of comb-shaped electrodes ₁₃ 1, 13 ₂ on the insulating substrate 11. The electrodes ₁₃ 1, 13 ₂ may for example in the case, configured with no need to consider the oxide film on the surface Au.

  Next, a terminal plated with Sn plating or Sn-based plating, for example, Sn-Ag plating, is left on the terminal for several tens of hours or hundreds of hours at room temperature or a temperature near the operating temperature of an electronic device. Grow whiskers. The grown whisker is taken out from the root and used as a test sample.

  In this case, in order to obtain whiskers generated in different situations, a plurality of samples having different plating bases are prepared. For example, a Ni base layer is provided on the surface of a terminal made of brass and then Sn-based plating is performed, or a surface of a terminal made of brass is directly subjected to Sn-based plating.

  In addition, in order to obtain whiskers that occur in the same situation as the usage state of electronic equipment, whiskers are generated by leaving a male connecting member provided with a terminal and a female connecting member having a recess fitted at room temperature. Let In this case, the whisker is generated due to external stress at the time of fitting. Therefore, the whisker is generated in a state close to an actual situation.

3 and 4 are conceptual illustrations of the whisker installation state. FIG. 3 (a) shows the root of the whisker 14 on one side surface of the pair of electrodes 12 ₁ and 12 ₂ shown in FIG. 2 (a). The end portion is in contact and the side surface of the whisker 4 is in contact with the shoulder portion of the other electrode. In FIG. 3B, the tip of the whisker 14 is in contact with one side surface of the pair of electrodes 12 ₁ , 12 ₂ and the side surface of the whisker 14 is in contact with the shoulder portion of the other electrode. Is. Further, FIG. 3 (c) is obtained by installing a whisker 14 so as to straddle the pair of electrodes ₁₂ 1, 12 ₂ of the surface.

FIG. 4 (d) contacting the plurality of whiskers 14, one end only of the one electrode ₁₂ 1, 12 ₂ side of each whisker 14 between the pair of electrodes 12 ₁ and the electrode 12 ₂ and the other Are installed in a state in which the end portions or side surfaces thereof are in contact with each other. Figure 4 (e) are those opposite ends one whisker 14 between the electrode 12 ₁ and the electrode 12 ₂ is installed is pushed in contact with the side surfaces of the electrodes ₁₂ 1, 12 _2.

FIG. 4 (f) is obtained by installing a whisker 15 so as to straddle the pair of comb-shaped electrodes ₁₃ 1, 13 ₂ of the surface shown in FIG. 2 (b). This is an installation state when the whisker 15 is longer than the above-described whisker 14.

  After installing the whisker in the above installation state, a predetermined voltage is applied to the whiskers 14 and 15 from the DC power source 21 via the resistor 22, and the presence or absence of current flowing between the electrodes is examined by the ammeter 23. If the current flows, it is judged that the whisker has many defects in the surface oxide film that causes a short circuit. If the current does not flow, the whisker has no defects in the surface oxide film. Judge that there is no problem.

In addition, in the case of the installation state shown in FIG.4 (e), it electrically short-circuits and an electric current flows. This is presumably because defects occur in the surface oxide film at the end of whisker 14 when one whisker 14 is pushed in such a way that both ends thereof are in contact with the side surfaces of the pair of electrodes 12 ₁ , 12 ₂ . However, since the probability that the whisker enters so as to be in contact with the end of the electrode is extremely rare, the test by this installation is not essential.

As described above, in the embodiment of the present invention, the presence / absence of current is only measured using a whisker setting jig having a simple configuration, and therefore, it is possible to investigate without using an electron microscope.
Therefore, preprocessing for microscopic observation is not required, and it is not necessary to spend time at high magnification to examine the entire whisker. This makes it possible to easily investigate the state of the surface oxide film without taking time and cost.

  The reliability of the electronic component can be easily evaluated by the whisker short-circuit test of the present invention. For example, an electronic component using a terminal with whisker that has been found to have defects in the surface oxide film will short-circuit between the terminals because the whisker is short-circuited, which adversely affects the electrical reliability of the electronic component. become. Therefore, the terminal where the whisker is short-circuited cannot be used as an electronic component at that time.

  On the other hand, if the surface oxide film is not deficient, even if the whisker is on the electrode, there is almost no short-circuit, and thus the terminal where the whisker is generated can be used as an electronic component.

  Based on the above, a whisker short-circuit test method according to Embodiment 1 of the present invention will be described next with reference to FIGS. FIG. 5A is an explanatory diagram of the occurrence of whiskers. The terminal 30 obtained by applying the Sn plating 33 to the brass 31 with the Ni base 32 attached thereto is left at, for example, 85 ° C. for 500 hours to thereby form the terminal 30. The whisker 35 is generated from the surface. Reference numeral 34 in the drawing is a seal member that supports the terminal 30.

  Next, a sample is prepared by scooping up and taking out the root of the whisker 36 with a sharp needle-like tool having a tip of 0.3 mm or less while enlarging with a microscope. The shape of the whisker taken out was a straight line having a length of 450 μm or 250 μm and a diameter φ of 5 μm.

  FIG. 5B is a conceptual cross-sectional view of the extracted whisker, and a natural oxide film 36 having a thickness of several nanometers is formed on the surface of the whisker 35. Note that the end portion of the base of the whisker 35 is in a state without the natural oxide film 36.

  FIG. 6 is a diagram for explaining the configuration of the whisker test apparatus according to the first embodiment of the present invention. A fixed resistance of 1 kΩ is used as the resistor 22 and a voltage of 12 V is applied from the DC power source 21.

FIG. 7 (a) is an explanatory view of a whisker installation state, in which a whisker 35 having a length of 450 μm is set in the same installation state as in FIG. 3 (a), and the electrode 12 ₁ , 12 ₂ has a line width. A 0.07 mm Au electrode was used. Here, the distance between the electrodes was set to 0.4 mm.

  In this state, a voltage of 12 V was applied and the current value flowing through the 1 kΩ fixed resistor was examined for 15 minutes by the ammeter 23. As a result, no current flowed between the electrodes. Therefore, the investigated whisker 35 did not conduct even when one end of the whisker 35 was in contact with one end of the Au electrode. Therefore, the whisker 35 was not conducting, and there was no defect in the surface oxide film. I understood.

FIG. 7B shows two whiskers 35 having a length of 250 μm in the same installation state as FIG. 4D. Here, the interval between the electrodes 12 ₁ and 12 ₂ having a line width of 0.1 mm is 0.45 mm. In this state, a voltage of 12 V was applied and the current value flowing through the 1 kΩ fixed resistor was examined for 15 minutes by the ammeter 23. As a result, no current flowed between the electrodes. Therefore, the investigated whisker 35 did not conduct even when one end of the whisker 35 was in contact with one end of the Au electrode. Therefore, the whisker 35 was not conducting, and there was no defect in the surface oxide film. I understood.

  From this test result, when a Ni base is used as the base for the brass, even if the whisker 35 is generated, the surface oxide film is not lost. Therefore, even the terminal where the whisker is generated can be used as an electronic component. it can.

Next, a whisker test method according to the second embodiment of the present invention will be described with reference to FIGS.
FIG. 8 is a diagram illustrating the configuration of the whisker test apparatus according to the second embodiment of the present invention. A variable resistor of 0.5 kΩ, 1 kΩ, or 105.5 kΩ is used as the resistor 22, and 3.3 V is supplied from the DC power supply 21. Apply a voltage of.

FIG. 9 is an explanatory diagram of the whisker installation state of the second embodiment of the present invention. Here, since the whisker 37 as a sample is long, the above-described installation method of FIG. A pair of comb-shaped electrodes ₁₃ 1 made of Au in this case, 13 ₂ of the line width is the spacing between adjacent electrodes 13 ₁ and the electrode _{13. 2} in a state in which the combination together with 0.05mm is 0.18 mm.

  The whisker 37 in this case is obtained by direct Sn plating on a brass terminal, and the whisker 37 taken out by scooping the base has a straight line bent at several places with a length of 1.2 mm and a diameter φ of 4 μm. It was a whisker.

In such an installation state, a voltage of 3.3 V was first applied between the electrodes with the maximum resistance, and when current did not flow through the whisker 37, the resistance was gradually lowered. As a result, the maximum current in 105.5kΩ does not flow, upon reaching a 1kΩ gradually lowering the resistance, 3mA DC current flows between the electrodes, the electrodes ₁₃ 1, 13 ₂ even whiskers 37 also completely I was able to get continuity.

The installation state of whiskers 37 was confirmed microscopically, the electrode 13 1 at a plurality of points of whiskers 37 is _bent, 13 ₂ are in contact with, it was found that is taken conductive at this point. Therefore, it was found that when the whisker 37 is bent, the surface oxide film is missing, and when the surface oxide film is missing, the risk of the whisker 37 falling into the electronic device is high.

  From this test result, it was found that whisker 37 in which the surface oxide film was partially lost is likely to occur when brass is directly plated without providing a base. Therefore, there is a problem in using such a terminal generated by the whisker 37 as an electronic component.

1 is a configuration explanatory diagram of a whisker test apparatus according to an embodiment of the present invention. FIG. It is a notional block diagram of a whisker installation jig. It is a conceptual explanatory drawing of the installation state of a whisker. It is a conceptual explanatory drawing of the other installation state of a whisker. It is explanatory drawing of the whisker in Example 1 of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is structure explanatory drawing of the whisker test apparatus of Example 1 of this invention. It is explanatory drawing of the installation state of the whisker in Example 1 of this invention. It is explanatory drawing of the test method of the whisker of Example 2 of this invention. It is explanatory drawing of the installation state of the whisker in Example 2 of this invention.

Explanation of symbols

10 whisker installation jig 11 insulating substrate 12 ₁ , 12 ₂ , 13 ₁ , 13 ₂ electrode 14, 15 whisker 21 DC power supply 22 resistor 23 ammeter 30 terminal 31 brass 32 Ni base 33 Sn plating 34 seal member 35 whisker 36 nature Oxide film 37 whisker

Claims (5)

An installation step of installing whisker generated on a member plated with tin between the electrodes so as to be in contact with at least one electrode of the pair of electrodes;
A method for evaluating the reliability of an electronic component, comprising: an inspection step of applying a voltage between the electrodes to inspect for the presence or absence of a current flowing between the electrodes. The electronic component reliability evaluation method according to claim 1, wherein, in the installation step, the whisker is installed across the pair of electrodes. The electronic component reliability evaluation method according to claim 1, wherein, in the installation step, the plurality of whiskers are installed such that each of the whiskers contacts only one electrode of the pair of electrodes. The method for evaluating the reliability of an electronic component according to claim 1, wherein a voltage applied in the inspection step is 20 V or less. The method for evaluating reliability of an electronic component according to any one of claims 1 to 4, wherein the whisker is a whisker generated under the same conditions as the usage state of the electronic component.

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