JP2010025243A - Screw for fixing electronic component and electronic control apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a screw for fixing an electronic component capable of preventing a whisker from being generated, and an electronic control apparatus. <P>SOLUTION: A head 22 of a screw for fixing a connector of which the head of the screw is soldered after the connector 72 is screw-locked to a substrate 24 is soldered so as to cover the head by a film thickness not smaller than a predefined film thickness at which the whisker is not generated. The height H and the corner radius R of the head of the screw 22 for fixing the connector which standardizes the surface of the substrate are set at a value which enables soldering so as to cover the head by a film thickness not smaller than a predefined film thickness so that the generation of the whisker is prevented by being soldered at a film thickness not smaller than a predefined film thickness at the corner of the head. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electronic component fixing screw for fixing an electronic component and an electronic control device, and more specifically, an electronic component fixing screw capable of preventing the occurrence of whiskers and an electronic control including the electronic component fixing screw. Regarding equipment.

  FIG. 1 is a diagram illustrating an example of an appearance of a solder dip surface of an ECU (Electric Control Unit) according to a conventional technique. FIG. 2 is a diagram showing another example of the appearance of the solder dip surface of the ECU according to the conventional technique. In FIG. 1, the connector 1 indicated by broken lines is attached to the mounting surface of the substrate 2 by connector fixing screws 5 at three locations. In FIG. 2, the connector 3 is attached to the mounting surface of the substrate 4 at two locations by the connector fixing screws 5, but a part of the connector 3 is attached in a state protruding from the substrate 4. After the connectors 1 and 3 are screwed to the substrates 2 and 4 by the connector fixing screws 5, the heads of the connector fixing screws 5 are flow soldered.

  FIG. 3 is a view showing a connector fixing screw 5 according to the prior art. 3A is a view of the connector fixing screw 5 as viewed from the head side, and FIG. 3B is a view of the connector fixing screw 5 as viewed from a direction orthogonal to the central axis of the screw. The screw part is “JIS B 1007 type 2 nominal diameter 3” according to Japanese Industrial Standard (hereinafter referred to as “JIS”), and the cross hole of the screw head is “JIS B 1012H type cross hole 2 type”. The height h of the screw head is 1.4 mm to 1.6 mm, and the corner radius r of the head is 0.8 mm.

  FIG. 4 is a cross-sectional view of a connector fixing screw 5 having a head soldered thereto according to a conventional technique. FIG. 5 is a diagram showing soldering at the corners of the head of the connector fixing screw 5. FIG. 5A is an enlarged photograph showing soldering at the corner of the head of the screw, and FIG. 5B is an enlarged photograph showing solder film at the corner of the head. Soldering tends to be thin at the corner, and the solder film thickness t remaining at the corner of the screw head is 1.5 μm on average.

  Of the solder soldered to the head of the connector fixing screw 5, a portion having a thin layer thickness is easily oxidized, and thus whiskers are easily generated. A whisker is a whisker-like structure generated on a metal surface. On the plating surface, it is known that a single crystal of tin, which is the same component as the base metal, grows from the root. Some whiskers are as long as 500 μm. As lead-free solder is used as it is now, the whisker problem is significant. In order to prevent oxidation, the head of the soldered connector fixing screw 5 is coated.

  Patent Document 1 discloses a solder including a screw head of a printed wiring board in order to prevent a short circuit from occurring when the solder is peeled off and dropped even if a crack occurs in the solder attached to the screw head. It is disclosed to coat a surface. Specifically, the electronic component mounted on the mounting surface of the substrate is fixed by screws from the solder surface which is the other surface of the substrate. The head of the screw exposed to the solder surface is soldered by flow soldering the solder surface. Thereafter, the solder surface including the head of the screw is coated with a coating agent.

  In Patent Document 2, in order to improve the connection strength between a printed circuit board and an electronic component and to prevent the substrate or the electronic component from warping, some of a plurality of screws for fixing the electronic component to the substrate are disclosed. It is disclosed that after screwing only with a screw, the head of the screwed screw is flow soldered. After the substrate and the electronic component are cooled to a predetermined temperature, the electronic component is screwed to the substrate with the remaining screws.

  Patent Document 3 discloses a configuration for preventing a mounting screw of a connector attached to a motor from being loosened. The tapered engagement hole provided in the bottom of the connector and the female screw provided in the upper wall of the motor are brought into a matched state, and a flat head screw is inserted into the engagement hole, and the connector is screwed to the motor. . The countersunk screw used for screwing is configured so that it cannot move in the loosening direction.

  Patent Document 4 discloses that when lead wires of a semiconductor chip are externally plated using lead-free solder, the lead wires have a certain thickness or more in order to suppress the growth of whiskers that cause short-circuiting of the lead wires. It is disclosed that plating is applied. This is because the thin outer plating on the lead surface causes the whisker to grow.

JP 2006-245451 A JP 2006-24614 A Japanese Patent No. 2580284 JP 2006-351907 A

  However, the coating of the head of the soldered connector fixing screw 5 is costly. In Patent Documents 1 to 3, a configuration for preventing the occurrence of whiskers is not disclosed. Patent Document 4 discloses that whisker is prevented from occurring on the lead surface, but does not disclose that whisker is prevented from occurring on the screw head.

  An object of the present invention is to provide an electronic component fixing screw and an electronic control device that can prevent the occurrence of whiskers.

The present invention (1) is an electronic component fixing screw for fixing an electronic component and soldering the head,
The shape and height of the head is a shape and height in which the solder formed so as to cover the head becomes a film thickness equal to or greater than a predetermined film thickness when attached to the substrate and soldered. This is an electronic component fixing screw.

  The present invention (9) is an electronic control device comprising the electronic component fixing screw.

  According to the present invention (1), the shape and height of the head of the electronic component fixing screw to which the electronic component is fixed and the head is soldered are determined in advance by attaching the electronic component fixing screw to the substrate. Since the solder is formed in a shape and height so as to cover the head with a film thickness equal to or greater than the film thickness, the occurrence of whiskers can be prevented.

  Moreover, according to this invention (9), since the said electronic component fixing screw is provided, it can be set as the electronic control apparatus provided with the electronic component fixing screw which can prevent generation | occurrence | production of a whisker.

  FIG. 6 is a cross-sectional view of the connector fixing screw 21 according to the first embodiment of the present invention. FIG. 6 shows a connector fixing screw 21 which is an electronic component fixing screw attached to the substrate 24. In the connector fixing screw 21, a stepped portion 27 is formed between the head portion 22 and the screw portion 28. A cross hole 25 for turning the connector fixing screw 21 with a screwdriver or the like is formed in the head portion 22 of the connector fixing screw 21. The head portion 22 of the connector fixing screw 21 has a convex shape having the same central axis as the screw portion 28. The peripheral edge 29 of the rounded top is smoothly connected to the outer peripheral edge side surface by an arc having a radius R, which will be described later, in a cross section cut by a plane including the central axis of the screw. The height H of the head portion 22 of the connector fixing screw 21 with respect to the surface of the substrate 24 is 1 mm or less, and the radius R of the corner portion 29 of the head portion 22 is 0.5 mm or more.

  The stepped portion 27 has a cylindrical shape having the same central axis as the screw portion 28, and the diameter of the stepped portion 27 is smaller than the diameter of the screw head 22 and larger than the outer diameter of the screw portion 28. If the height H of the head portion 22 is reduced in order to secure the solder film thickness, the depth of the cross hole 25 may be insufficient, and the driver bit hook may be insufficient when the screw is turned by a driver. In order to ensure the depth of the cross hole 25, a stepped portion 27 is provided. The stepped portion 27 is accommodated in the through hole 23 formed in the substrate 24. The diameter of the through-hole 23 that is the housing portion is slightly larger than the diameter of the stepped portion 27.

  When the height of the stepped portion 27 is low, a cylindrical recess having a diameter slightly larger than the diameter of the stepped portion 27 and having the same depth as the height of the stepped portion 27 is formed from the solder surface 26 side. The relief hole of the screw portion 28 may be formed on the central axis of the cylindrical recess. The shape of the recess is cylindrical for ease of processing, but is not limited to the cylindrical shape.

  Since the whisker is generated by oxidation at a portion where the solder film thickness is thin, the solder film thickness must be a predetermined film thickness at which no whisker is generated, for example, 5 μm or more. By soldering the entire head portion 22 of the connector fixing screw 21 with a film thickness of 5 μm or more, it is possible to prevent whiskers from occurring in the head portion 22. Accordingly, the height H of the head portion 22 and the corner radius R of the head portion 22 are values that allow the entire head portion 22 to be soldered with a film thickness of 5 μm or more.

  FIG. 7 is a sectional view of a connector fixing screw 31 according to the second embodiment of the present invention. The head 32 of the connector fixing screw 31 is accommodated in a cylindrical recess 35 formed in the substrate 33. The cylindrical recess 35 has an opening on the solder surface 34 side. The diameter of the cylindrical recess 35 is slightly larger than the diameter of the head 32 so that the head 32 can be accommodated. The depth of the cylindrical recess 35 is shallower than the thickness of the substrate 33. The height of the head 32 is the same as the depth of the cylindrical recess 35 or lower than the depth of the cylindrical recess 35.

  When the height of the head 32 is lowered, the depth of the cross hole 38 formed in the head 32 is insufficient. By providing the stepped portion 36 between the head portion 32 and the screw portion 39, the cross hole 38 can be formed in a portion obtained by adding the stepped portion 36 to the head portion 32, and the depth of the cross hole 38. Is secured. In the substrate 33, a through hole 37 for accommodating the stepped portion 36 is formed on the central axis where the cylindrical recess 35 is formed. The diameter of the through hole 37 is slightly larger than the diameter of the stepped portion 36. Since the head portion 32 is accommodated in the cylindrical recess 35, it is possible to prevent the solder film thickness formed at the corner portion of the head portion 32 from becoming thin.

  In the example shown in FIG. 7, the entire head 32 is accommodated in the cylindrical recess 35, but since the depth of the cylindrical recess 35 is shallower than the height of the head 32, a part of the head 32 is It may protrude from the solder surface 34. Since the height of the head portion 32 protruding from the solder surface 34 is lower than that when the head portion 32 is attached to the substrate 33 without forming the cylindrical recess 35, it is possible to prevent a thin portion from being generated in the solder film. it can.

  FIG. 8 is a sectional view of a connector fixing screw 41 according to the third embodiment of the present invention. The shape of the head portion 42 of the connector fixing screw 41 is a plate shape that is the shape of the head portion of a countersunk screw. The substrate 43 is formed with a tapered through hole 44 with which the head portion 42 is pressed. Since the head 42 is dish-shaped, the head 42 is flush with the solder surface 45 by making the diameter of the opening of the through hole 44 formed in the solder surface 45 equal to the diameter of the head 42. Be placed. Since the head portion 42 does not protrude from the solder surface 45, it is easy to perform soldering with a predetermined film thickness or more, and the occurrence of a thin portion is suppressed.

  Since the substrate 43 has a tapered through hole 44, the diameter of the opening formed in the connector mounting surface 46 on the opposite side of the solder surface 45 is smaller than the diameter of the threaded portion 48 to be inserted. In some cases, the screw 41 cannot be inserted. In this case, hole processing for forming an opening 47 which is an escape hole for the screw portion 48 is performed.

  FIG. 9 is a diagram showing a solder film formed on the head portion 51 of a soldered connector fixing screw (hereinafter also referred to as “screw”). FIG. 9A is a photograph showing the head 51 of the screw that is soldered. FIG. 9B is a photograph showing a cross section of the screw head 51 cut along a cutting plane line AA in the central axis direction of the screw portion. FIG. 9C is an enlarged photograph of the corner 52 of the screw head 51. In the screw head 51 shown in FIG. 9A, the numerical values of the height H of the head 51 of the connector fixing screw and the radius R of the corner 52 of the head 51 with respect to the solder surface of the substrate are The entire portion 51 has a solder film thickness of 5 μm or more and is a value that can be soldered.

  FIG. 9B shows that the solder film thickness tends to be thinner at the corner portion 52 than at the peripheral portion. When lead-free solder 83 shown in FIG. 9C is oxidized, volume expansion occurs, and compressive internal stress is generated in the solder layer 83. The internal stress tends to concentrate on the corner portion 52 that is a thin portion of the solder film 83. Since whisker is generated by internal stress, it is likely to be generated at the corner 52. In a portion where the solder film pressure is secured to 5 μm or more, the internal stress is relieved, so that whiskers are hardly generated.

  FIG. 10 is a sectional view of a connector fixing screw 21 according to the fourth embodiment of the present invention. The entire head portion 22 of the soldered connector fixing screw 21 is covered with a tape 61 that is a whisker dropout prevention portion. In the example shown in FIG. 10, the tape 61 is affixed, but the head 22 may be sealed with a sealing material, or the cap may be put on the head 22. By keeping the solder film thickness above a certain thickness, the generation of whiskers is suppressed. However, once the whisker has been dropped and scattered on the electronic component, it causes a short circuit. By covering the entire head portion 22 with the tape 61, it is possible to prevent the whisker that has occurred by any chance from falling off and scattering to the electronic component.

  Thus, the shape and height of the head 22 of the connector fixing screw 21 to which the connector 72 is fixed and the head 22 is soldered are determined in advance by attaching the connector fixing screw 21 to the substrate 24. Since the solder is formed in a shape and height so as to cover the head 22 with a film thickness equal to or greater than the film thickness, the occurrence of whiskers can be prevented.

  Furthermore, since the predetermined film thickness is 5 μm, soldering can be performed with a film thickness of 5 μm or more, and the occurrence of whiskers can be prevented.

  Further, the connector fixing screw 21 includes a stepped portion 27 provided between the head portion 22 and the screw portion 28 of the connector fixing screw 21 and accommodated in the through hole 23 formed in the substrate 24. Therefore, the depth of the cross hole 25 is supplemented, and it is possible to prevent the driver bit from being insufficient when the screw is turned by the driver.

  Further, the substrate 33 communicates with the through hole 37 for accommodating the stepped portion 36, has a diameter larger than the diameter of the through hole 37, and has a cylindrical shape that accommodates at least a part of the head 32 of the screw 31. The surface of the head 32 of the screw 31 that is in contact with the substrate 33 is pressed against the bottom surface that connects the side surface of the cylindrical recess 35 and the side surface of the through hole 37. It can prevent that a thin part generate | occur | produces.

  Furthermore, since the head 32 of the connector fixing screw 31 has a height that does not protrude from the surface 34 of the surface of the substrate 33 to which the head 32 is attached, it is possible to prevent the solder film thickness from being reduced. it can.

  Furthermore, since the shape of the head portion 42 of the connector fixing screw 41 is a countersunk shape that is the shape of the head portion of a countersunk screw, the head portion 42 of the screw 41 and the solder surface 45 are disposed on the same plane. Can do. Therefore, generation | occurrence | production of a thin part is suppressed further.

  Furthermore, since the solder formed so as to cover the head portion 22 of the connector fixing screw 21 is covered with the tape 61 that prevents the whisker generated from the solder from dropping off, even if a whisker is generated, the generated whisker is generated. Can be prevented from falling off.

  Further, the radius R of the corner portion 29 of the head portion 22 of the connector fixing screw 21 is 0.5 mm or more, and the height H of the head portion 22 of the connector fixing screw 21 is 1 mm or less. The head portion 22 of the working screw 21 can be soldered with a film thickness of 5 μm or more, and the occurrence of whiskers can be prevented.

  FIG. 11 is a diagram schematically showing a configuration of an ECU 71 according to the fifth embodiment of the present invention. The ECU 71, which is an electronic control device, includes a connector fixing screw 21 that is soldered to a predetermined thickness or more on the entire surface of the head 22. Therefore, it can be set as ECU71 provided with the screw 21 for connector fixation which can prevent generation | occurrence | production of a whisker.

  Thus, since ECU71 is provided with connector fixing screw 21, it can be set as ECU71 provided with connector fixing screw 21 which can prevent generation of a whisker.

It is a figure which shows an example of the external appearance of the solder dip surface of ECU by a prior art. It is a figure which shows the other example of the external appearance of the solder dip surface of ECU by a prior art. It is a figure which shows the connector fixing screw 5 by a prior art. It is sectional drawing of the connector fixing screw 5 by which the head was soldered by the prior art. It is a figure which shows the soldering of the corner | angular part of the head of the screw 5 for connector fixation. It is sectional drawing of the screw 21 for connector fixation which is the 1st Embodiment of this invention. It is sectional drawing of the screw 31 for connector fixation which is the 2nd Embodiment of this invention. It is sectional drawing of the screw 41 for connector fixation which is the 3rd Embodiment of this invention. It is a figure which shows the solder film of the head part 22 of the screw 21 for connector fixing soldered. It is sectional drawing of the screw 21 for connector fixation which is the 4th Embodiment of this invention. It is a figure which shows typically the structure of ECU71 which is the 5th Embodiment of this invention.

Explanation of symbols

1, 3, 72 Connector 2, 4, 24, 33, 43 Substrate 5, 21, 31, 41 Connector fixing screw 22, 32, 42, 51 Connector fixing screw head 23, 37, 44 Through hole 25, 38 Cross hole 26, 34, 45 Solder surface 27, 36 Stepped portion 28, 39, 48 Screw portion 29, 52 Corner portion 35 Cylindrical recess 46 Connector mounting surface 47 Opening portion 61 Tape 71 ECU
81 Copper base 82 Tin-lead alloy layer 83 Lead-free solder 84 Solder oxide

Claims (9)

An electronic component fixing screw for fixing an electronic component and soldering the head,
The shape and height of the head is a shape and height in which the solder formed so as to cover the head becomes a film thickness equal to or greater than a predetermined film thickness when attached to the substrate and soldered. An electronic component fixing screw characterized by that.   The electronic component fixing screw according to claim 1, wherein the predetermined film thickness is 5 μm. A stepped portion is provided between the head and the screw portion,
The electronic component fixing screw according to claim 1, wherein the stepped portion is accommodated in an accommodating portion formed on the substrate. The substrate communicates with a through-hole for penetrating a screw portion, and has a diameter larger than the diameter of the through-hole, and a housing portion that houses at least a part of the head is formed.
The surface in contact with the substrate among the surfaces of the head is in pressure contact with a bottom surface that connects a side surface of the housing portion and a side surface of the through hole. The electronic component fixing screw described.   5. The electronic component fixing screw according to claim 4, wherein the head has a height that does not protrude from a surface of the substrate.   3. The electronic component fixing screw according to claim 1, wherein the shape of the head is the shape of a head of a countersunk screw.   The solder formed so as to cover the head is covered with a whisker drop-off prevention unit that prevents the whisker generated from the solder from dropping off. Screw for fixing electronic parts.   3. The electronic component fixing screw according to claim 1, wherein a radius of a corner portion of the head is 0.5 mm or more, and a height of the head is 1 mm or less.   An electronic control device comprising the electronic component fixing screw according to claim 1.