Tip structure and contact pin

Abstract

To provide a tip structure which has and can maintain a small curvature radius of an apex.SOLUTION: A tip structure of the present invention has an apex used to contact a target and verify electrical continuity, and comprises a base material made of an iron alloy containing 3 mass% or more of Cr and provided with an edge, and a conductive layer covering the base material, where the apex has a minimum curvature radius of 5 μm or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a tip structure and a contact pin including the tip structure. [Background technology]

[0002] When inspecting electrical components such as IC packages, quality control is performed by checking continuity. For example, Patent Document 1 discloses an electrical connection inspection device that makes electrical contact with the inspection object to check the electrical connection. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4045084 Summary of the Invention [Problem to be solved by the invention]

[0004] Contact pins are known as a component of testing equipment used to check electrical continuity. A contact pin has a tip, which contacts the test object to check electrical continuity. Specifically, the tip of the contact pin has a vertex, which contacts the solder ball of the IC chip to check electrical continuity.

[0005] Conventionally, beryllium copper (BeCu) or carbon tool steel (SK material) has been used as the base material for the tip of a contact pin. When using BeCu or SK material as the base material, an edge is formed on the BeCu or SK material, and the area including the edge is first nickel-plated and then gold-plated to form the apex. Because BeCu and SK materials are not corrosion-resistant, oxidation can progress to the interior. Therefore, strong chemical polishing is required as a pretreatment for plating to remove the oxidized areas. However, strong chemical polishing erodes the base material, increasing the radius of curvature of the edge to approximately 10 μm. This large radius of curvature makes it difficult for the plated edge, i.e., the apex of the tip, to penetrate into the solder ball, making it difficult to reliably test for electrical continuity.

[0006] Palladium alloys are also known as the base material for the tip of contact pins. When using a palladium alloy as the base material, neither plating nor chemical polishing is required. Therefore, when using a palladium alloy as the base material, the edge formed on the base material can be used as the apex for contact, allowing for a small radius of curvature of the apex. However, palladium is easily alloyed with tin in the solder ball and wears easily. Therefore, when the apex of a palladium alloy contact pin is repeatedly brought into contact with a solder ball, the radius of curvature of the apex increases, making it difficult to stably test conductivity.

[0007] An object of the present invention is to provide a tip structure that has a small radius of curvature at the apex and that can maintain the small radius of curvature at the apex, and a contact pin having such a tip structure. [Means for solving the problem]

[0008] The present invention relates to the following tip structure and contact pin having the tip structure. [1] A tip structure having a vertex that is used for contacting and checking electrical continuity, the tip structure being made of an iron alloy with a Cr content of 3% by mass or more, including a base material having an edge and a conductive layer covering the base material, and the minimum radius of curvature of the vertex is 5 μm or less. [2] The tip structure according to [1], wherein the conductive layer contains at least one metal selected from gold, silver, tin, and platinum group metals. [3] The tip structure according to [1] or [2], wherein the conductive layer comprises two or more layers. [4] The tip structure according to [2] or [3], wherein the conductive layer further contains at least one metal selected from palladium, cobalt, and nickel. [5] The tip structure according to any one of [1] to [4], further comprising a nickel layer between the base material and the conductive layer. [6] The tip structure according to any one of [1] to [5], wherein the base material has a Vickers hardness of 400 HV or more. [7] The tip structure according to any one of [1] to [6], wherein the conductive layer has a Vickers hardness of 1000 HV or less. [8] A contact pin having the tip structure described in any one of [1] to [7]. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a tip structure that has a small radius of curvature at the apex and that can maintain the small radius of curvature at the apex, and a contact pin having this tip structure. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing a contact pin. [Figure 2] FIG. 2 is a partial cross-sectional view of the tip structure of the contact pin. [Figure 3] FIG. 3A is a diagram showing the results of the wear resistance test of an example, and FIG. 3B is a diagram showing the results of the wear resistance test of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Contact pin] FIG. 1 is a diagram illustrating a contact pin 10. As shown in FIG. 1, the contact pin 10 has a tip structure 11. FIG. 2 is a partial cross-sectional view of the tip structure 11. As shown in FIG. 2, the tip structure 11 has an apex 14 used for checking electrical continuity. The tip structure 11 has a base material 12 made of an iron alloy (e.g., stainless steel) with a Cr content of 3 mass % or more, and a conductive layer 13 covering the base material 12 (edge ​​12a). Here, the minimum radius of curvature of the apex 14 is 5 μm or less, and it is more preferable that the minimum radius of curvature of the apex 14 is 4 μm or less. By having the minimum radius of curvature of the apex 14 be 5 μm or less, the apex 14 can easily bite into the solder ball 2, enabling stable electrical continuity checking. The minimum radius of curvature of the apex 14 can be measured using a laser microscope. The "vertex" here refers not only to the state formed from the conductive layer 13, but also to the state where, for example, the conductive layer 13 is worn away and the base material 12 (edge ​​12a) is exposed from the conductive layer 13. In other words, the "vertex" refers to the point on the contact pin that comes into contact with the solder ball 2 of the IC chip 1. There may be one or more vertices 14. In this embodiment, the tip structure 11 and the contact pin 10 have a plurality of vertices 14.

[0012] A contact pin 10 configured with the tip structure 11 described above can easily bite into, for example, a solder ball 2 of an IC chip 1, enabling stable conduction confirmation, as shown in FIG. 1. The contact pin 10 has the tip structure 11 at one end and also has the other end opposite the tip structure 11. The two ends are electrically connected, and the length between the two ends changes as the biasing member (spring) 15 expands and contracts. The contact pin 10 can be used while supported by a support (socket).

[0013] The base material 12 and conductive layer 13 of the tip structure 11 of the contact pin 10 will be described in detail below.

[0014] (base material) The base material 12 is made of an iron alloy with a Cr content of 3 mass % or more, and is preferably made of, for example, stainless steel. In this embodiment, the base material 12 has an edge 12a, which forms a vertex 14 together with the conductive layer 13.

[0015] In this specification, stainless steel refers to stainless steel as defined in JIS G0203 4.3.8, i.e., steel with a Cr (chromium) content of 10.5 mass% or more and a carbon content of 1.2 mass% or less. In the present invention, the type of stainless steel is not particularly limited, and examples of the type of stainless steel include austenitic stainless steel and martensitic stainless steel.

[0016] The iron alloy of the base material 12 may have a Cr content of 3 mass% or more, preferably 10.5 mass% or more, and more preferably 13 to 15 mass%. The iron alloy of the base material 12 also has a carbon content of 1.2 mass% or less, and preferably 0.1 mass% or more.

[0017] Base material 12 made of an iron alloy with a Cr content of 3% by mass or more has a passive film on its surface, and oxidation does not progress to the interior of base material 12. Therefore, when covering the surface of base material 12 with conductive layer 13 by plating or the like, there is no need to perform strong chemical polishing as a pretreatment. Therefore, by using base material 12 made of an iron alloy with a Cr content of 3% by mass or more, the radius of curvature of edge 12a can be made small, and further, when covered with conductive layer 13, the radius of curvature of vertex 14 can be maintained small.

[0018] After the conductive layer 13 is formed on the surface, it is preferable that the base material surface does not have a passive film in order to ensure good conductivity of the base material 12 made of an iron alloy with a Cr content of 3% by mass or more. A thin passive film exists on the surface of the untreated base material 12 made of an iron alloy with a Cr content of 3% by mass or more. Therefore, although strong surface treatment such as chemical polishing is not necessary as a pretreatment when covering with the conductive layer 13, it is preferable to perform a surface treatment such as weak chemical polishing to a degree that can remove the passive film. Note that surface treatment (e.g., chemical polishing) may be performed as needed, and surface treatment is not necessarily required.

[0019] The radius of curvature of the edge 12a formed on the base material 12 may be adjusted appropriately so that the minimum radius of curvature of the vertex 14 (the conductive layer 13 covering the edge 12a) is 5 μm or less when the edge 12a is covered with the conductive layer 13. Therefore, the minimum radius of curvature of the edge 12a is preferably less than 5 μm, and more preferably less than 4 μm. The minimum radius of curvature of the edge 12a can be measured using a laser microscope.

[0020] The base material 12 may have one or more edges 12a. In this embodiment, the base material 12 has a plurality of edges 12a.

[0021] The base material 12 made of an iron alloy with a Cr content of 3 mass % or more preferably has a Vickers hardness of 400 HV or more, and more preferably 500 HV or more. A Vickers hardness of 400 HV or more suppresses wear of the edge 12a of the base material 12.

[0022] The base material 12 made of an iron alloy with a Cr content of 3% by mass or more may be quenched or unquenched. Quenching can be used to make the base material 12 made of an iron alloy with a Cr content of 3% by mass or more have a desired Vickers hardness. When the base material 12 is quenched, the Vickers hardness of the base material 12 (400 HV or more) refers to the Vickers hardness after quenching. Therefore, the Vickers hardness of the base material 12 before quenching may be less than 400 HV. The Vickers hardness of the base material 12 can be measured in accordance with JIS Z2244:2009.

[0023] If an iron alloy with a Cr content of 3% by mass or more contains silicon, it becomes hard and difficult to process, making it difficult to form the edge 12a. Therefore, it is preferable that an iron alloy with a Cr content of 3% by mass or more does not contain silicon. Specifically, it is preferable that the silicon content of an iron alloy with a Cr content of 3% by mass or less is 1% by mass or less.

[0024] (Conductive layer) The conductive layer 13 is a layer that covers the base material 12 (edge ​​12a). The conductive layer 13 plays a role in reducing the electrical resistance of the tip structure 11 (contact pin 10). It is preferable that the conductive layer 13 covers at least the edge 12a. In this embodiment, the conductive layer 13 covers the entire base material 12 including the edge 12a. The minimum radius of curvature of the conductive layer 13 (vertex 14) covering the edge 12a is 5 μm or less, and more preferably 4 μm or less. This makes it easier for the conductive layer 13 (vertex 14) covering the edge 12a to bite into the solder ball 2, enabling stable conductivity confirmation. The minimum radius of curvature of the conductive layer 13 (vertex 14) can be measured using a laser microscope.

[0025] There are no particular limitations on the material that constitutes the conductive layer 13, as long as it has conductivity that allows it to function as an electrical contact. Specific examples of the conductive layer 13 include layers containing at least one metal selected from gold (Au), silver (Ag), tin (Sn), platinum group metals (platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), and osmium (Os)), cobalt (Co), nickel (Ni), and bismuth (Bi). The conductive layer 13 may be an alloy layer containing two or more of the above elements, for example, an alloy layer selected from Au—Co, Au—Ni, Au—Ag, Au—Sn, Pd—Co, Pd—Ni, Pd—Ag, Rh—Ru, Pt—Ir, Pt—Rh, Sn—Ag, Sn—Cu, and Sn—Bi. The conductive layer 13 is preferably a layer containing one type of metal selected from gold (Au), silver (Ag), tin (Sn) and the platinum group metals (platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), osmium (Os)), a layer of an alloy containing palladium and cobalt (PdCo), or a layer of an alloy containing palladium and nickel (PdNi). Furthermore, the conductive layer 13 may be formed by laminating multiple layers, and may include two or more layers. When the conductive layer 13 is a laminate, the layer on the vertex 14 side that contacts the electrical component is the surface conductive layer, and the layer on the base material 12 side is the intermediate conductive layer. Examples of the surface conductive layer include the layers described above as the conductive layer. Examples of the intermediate conductive layer include a layer containing at least one metal selected from gold and palladium.

[0026] The conductive layer 13 may directly or indirectly cover the edge 12a of the base material 12 made of an iron alloy with a Cr content of 3% by mass or more. When the conductive layer 13 indirectly covers the edge 12a of the base material 12 made of an iron alloy with a Cr content of 3% by mass or more, a nickel layer is preferably present between the edge 12a of the base material 12 and the conductive layer 13. The nickel layer can be used to prevent the conductive layer 13 from peeling off from the base material 12. More specifically, the nickel layer is formed by plating while removing the passive film of an iron alloy with a Cr content of 3% by mass or more (nickel plating while decomposing the passive film in a Wood's bath). The nickel layer can be formed more easily than by directly plating the conductive layer onto the iron alloy, for example.

[0027] The conductive layer 13 may be formed by coating the base material 12 (edge ​​12a) by, for example, plating, vapor deposition, sputtering, or the like. Of these, it is preferable to coat the base material 12 (edge ​​12a) by plating. The plating method is not particularly limited. Examples of plating include electrolytic plating and electroless plating. When coating the base material 12 (edge ​​12a) with the conductive layer 13 by plating, the base material 12 having the edge 12a may or may not be chemically polished as a pretreatment.

[0028] The Vickers hardness of the conductive layer 13 is preferably 1000 HV or less. When the Vickers hardness of the conductive layer 13 is 1000 HV or less, the conductive layer 13 is prevented from becoming brittle, and a slight deformation of the base material 12 prevents the conductive layer 13 from cracking and peeling off from the base material 12. The Vickers hardness of the conductive layer 13 can be measured in accordance with JIS Z2244:2009.

[0029] The thickness of the conductive layer 13 is preferably 0.01 μm or more in order to ensure sufficient conductivity, and is preferably 5 μm or less in order to prevent the radius of curvature from becoming too large.

[0030] (effect) In tip structure 11 according to this embodiment, base material 12 made of an iron alloy with a Cr content of 3% by mass or more has edge 12a, and edge 12a is covered with conductive layer 13. This allows apex 14 to have a small radius of curvature of 5 μm or less, thereby stabilizing contact resistance. Furthermore, since iron alloys with a Cr content of 3% by mass or more are cheaper than palladium alloys, the costs of tip structure 11 and contact pin 10 having tip structure 11 can be reduced. [Example]

[0031] [Wear resistance test] A wear resistance test was conducted on the tips of the contact pins of the example and comparative example. The contact pins of the example had a stainless steel base material and a tip structure in which the base material with an edge was directly plated with gold. The minimum curvature radius of the gold plating layer (top) was 5 μm or less. On the other hand, the contact pins used in the comparative example had a base material made of BeCu, and the base material with an edge was first chemically polished, then plated with nickel, and finally plated with gold to form a tip structure. The minimum curvature radius of the gold plating layer (apex) was 10 μm.

[0032] The tip structures of these contact pins were brought into contact with solder balls 5,000 times, and the resistance value was measured each time. Note that new solder balls were used each time. The measurement results for the example are shown in the graph in Figure 3A, and the measurement results for the comparative example are shown in the graph in Figure 3B.

[0033] As can be seen from Figures 3A and 3B, the resistance value was low in the Example and high in the Comparative Example. Furthermore, the variation in resistance value was small in the Example and large in the Comparative Example. This is thought to be because the minimum radius of curvature of the gold layer (apex) in the Example was smaller than in the Comparative Example, causing the apex to be more deeply embedded in the solder ball.

[0034] Furthermore, as can be seen from Figure 3A, in the example, the resistance value remained low even after 5,000 contacts. This is thought to indicate that the apex was not worn and the minimum curvature radius remained small, indicating high wear resistance. Specifically, it is thought that wear was suppressed due to the low alloying between the tin in the solder ball and the gold-coated stainless steel base material. It is also thought that the stainless steel base material was not worn by mechanical force. [Industrial Applicability]

[0035] According to the present invention, the radius of curvature of the apex is prevented from becoming large, and stable continuity check can be performed over a long period of time, which is expected to improve the yield of electrical components and the like that are the subject of inspection. [Explanation of symbols]

[0036] 1 IC chip 2 solder balls 10 contact pins 11 Tip structure 12 Base material 12a Edge 13 Conductive layer 14 Vertex 15. Spring

Claims

1. A tip structure having a vertex that is used for contacting and checking continuity, a base material made of an iron alloy having a Cr content of 3 mass% or more and having an edge; a conductive layer covering the base material; Including, The minimum radius of curvature of the apex is 5 μm or less. Tip structure.

2. The tip of claim 1 , wherein the conductive layer comprises at least one metal selected from gold, silver, tin, and the platinum group metals.

3. The tip of claim 1 , wherein the conductive layer comprises two or more layers.

4. The tip of claim 2 , wherein the conductive layer further comprises at least one metal selected from palladium, cobalt, and nickel.

5. The tip of claim 1 further comprising a nickel layer between the base material and the conductive layer.

6. 2. The tip structure of claim 1, wherein the base material has a Vickers hardness of 400 HV or greater.

7. 10. The tip of claim 1, wherein the conductive layer has a Vickers hardness of 1000 HV or less.

8. A contact pin having the tip structure according to any one of claims 1 to 7.

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