JP2007059106A - Connection structure of press-fit terminal and base plate and designing method of press-fit terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a press-fit terminal with stable connection between the terminal and a through-hole and without risk of degradation of an insulating property of a base plate for a long time, as well as a designing method of the same capable of designing in a short time in designing a connection structure of the base plate and the press-fit terminal. <P>SOLUTION: In the connection structure of the terminal and the base plate made by inserting the press-fit terminal 1 in a press-fit state into a through-hole 3 of the base plate 2, the press-fit terminal is formed so that a contact load x[N] at insertion of the press-fit terminal into the through-hole is to be within a range expressed in formula (1): 40≤x≤290ä[Z-(A+2T+B)]/2}+20. In the formula (1), Z[mm] denotes an interpolar pitch (minimum) of the through-hole, A[mm] a diameter (maximum) of the through-hole, T[mm] a wall thickness (maximum) of the through-hole, and B[mm] a necessary insulation distance at least necessary for securing an insulation property between the terminal and wiring. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a press-fit terminal-substrate connection structure and a press-fit terminal design method incorporated in an electronic apparatus.

  Conventionally, as a method of fixing a terminal such as a printed circuit board and a terminal, a terminal called a press-fit terminal is inserted into a conductive through hole provided on the board, and the terminal is mechanically fixed without soldering. The method is known. The press-fit terminal is arranged between the guide part inserted into the through hole of the board, the mounting part to be mounted on the board connector, etc., and between the guide part and the mounting part, and has a width larger than the through hole diameter. A connecting portion to be formed.

  The press-fit terminal is inserted into the through hole of the board from the guide part, and the contact load is generated by press-fitting the connecting part with a width larger than the through hole diameter into the through hole, increasing the mechanical holding force. It is formed so as to obtain a stable electrical connection.

  The substrate is generally formed by laminating and pressing a large number of sheets impregnated with epoxy resin in which glass fibers are vertically and horizontally combined, and has a wiring circuit pattern made of a conductive member on the surface and through holes penetrating the front and back of the substrate. Is provided. The through hole of the substrate is plated with copper plating or the like from the wall of the inner peripheral surface of the through hole to the periphery of the through hole opening on the surface of the substrate. It is electrically connected to the circuit pattern.

  Boards used in control equipment used in harsh environments such as automobiles with large vibrations, high temperatures, and high humidity are required to secure press-fit terminals to the board in order to obtain high electrical connection reliability. It is necessary to secure. Thus, for example, a press-fit terminal is known in which the width of the press-fit connection portion is formed larger than the diameter of the through hole, and the press-fit terminal is increased to increase the holding force (see, for example, Patent Document 1).

JP 2004-127610 A

  However, in order to obtain a holding force with respect to the substrate as in the case of a conventional press-fit terminal, if the press-fitting joint of the press-fit connection portion is increased, there is a high possibility that the substrate is damaged when the press-fit terminal is press-fitted. This damage to the substrate is a factor that greatly deteriorates the substrate characteristics such as insulation.

  Further, when the substrate is used in a harsh operating environment such as a control device of an automobile, the electrical connection between the press-fit terminal and the through hole needs to be stable for a long time. That is, the contact resistance between the press-fit terminal and the through-hole of the substrate is required to be low and stable for a long time after the press-fit terminal is inserted.

  In addition, the connection between the press-fit terminal and the through-hole is electrically stable, and at the same time, even if whitening of the substrate occurs during use, a defect such as short-circuiting with the adjacent terminal occurs. It is required not to.

  When designing the shape of a press-fit terminal, consider the shape taking into account the holding force due to press-fitting scissors. However, it is unclear to what extent the press-fit scissors are set to obtain the optimum holding force. Conventionally, when designing a new press-fit terminal, the shape is determined by the experience and intuition of the designer. That is, a press-fit terminal is actually manufactured, inserted into the through-hole of the board, and subjected to various tests to evaluate the performance, and the evaluation result is fed back to change the shape etc. This process was repeated until a high-performance press-fit terminal was obtained. However, there is a problem that these series of operations are very time consuming and troublesome.

  The problem to be solved by the present invention is to provide a connection structure between a press-fit terminal and a through-hole, in which the connection between the terminal and the through-hole is stable and at the same time, there is no risk of deterioration of the insulating performance of the substrate over a long period of time. An object of the present invention is to provide a press-fit terminal design method that can be designed in a short period of time when designing a fit terminal.

In order to solve the above-mentioned problems, the present invention provides a press-fit terminal-board connection structure in which a press-fit terminal is inserted into a through-hole of a board in a press-fitted state as in the invention described in claim 1. The gist is that the press-fit terminal and the substrate are formed so that the contact load x [N] when the terminal is inserted into the through hole is within the range represented by the following formula (1). .
40 ≦ x ≦ 290 {[Z− (A + 2T + B)] / 2} +20 (1)
In the above equation (1), Z [mm] is the pitch between the through holes (minimum), A [mm] is the through hole diameter (maximum), T [mm] is the through hole wall thickness (maximum), and B [ mm] is the minimum necessary insulation distance necessary to ensure insulation between the terminal and the wiring.

  A press-fit terminal design method according to the present invention is a method for designing a press-fit terminal to be inserted into a through-hole of a board in a press-fitted state, as in the invention described in claim 2. The initial contact load that provides stable contact resistance after press-fitting the terminal and setting a stable contact resistance is set as the minimum contact load, and it is stable after the high-temperature and high-humidity test of the board as the insulation distance between the wiring pattern of the board and the through-hole. The required whitening distance to obtain the required insulation resistance, the allowable whitening distance from the required insulating distance and the through hole diameter, and press-fit multiple press-fit terminals with different contact loads into the through hole of the board to obtain the whitening length of the board To determine the relationship between the whitening length and the contact load, and based on this relationship, set the contact load corresponding to the allowable whitening distance as the maximum contact load. , To be less than the maximum contact load be at the contact load of the press-fit terminal is the minimum contact load above, it is an gist to design the press-fit terminal.

  According to the connection structure of the press-fit terminal and the substrate according to the present invention, the contact resistance between the press-fit terminal and the through-hole of the substrate is low and stable, and the contact resistance is stable over a long period of time. Even if whitening of the substrate occurs, there is no possibility that an insulating defect such as a short circuit with an adjacent terminal will occur.

  According to the method for designing a press-fit terminal according to the present invention, when designing the shape of the press-fit terminal, an optimum contact load can be set, so that a press-fit terminal having a desired performance can be easily obtained. It is possible to shorten the development time when making a new press-fit terminal.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. As shown in FIGS. 1 (a) and 1 (b), the press fit terminal 1 is inserted into the conductive through-hole 3 of the substrate 2 in a press-fit state. Is.

  As shown in FIG. 1 (a), the press-fit terminal 1 is formed such that the front end side is tapered as a guide portion 11, and the rear end side is formed as an attachment portion 12 for mounting to another terminal (not shown). Between the guide part 11 and the attachment part 12, it forms as the connection part 13 which contacts the inside of the through-hole 3, and is electrically connected. Various conductive paths (not shown) are formed on the surface of the substrate 2, and a plurality of through holes 3 penetrating the substrate 2 are provided as shown in FIG. A conductive layer 4 is formed on the inner peripheral surface and the opening peripheral edge of the through hole 3 by copper plating or the like, and the conductive layer 4 is connected to a conductive path on the surface of the substrate 2.

As shown in FIG. 1B, when the press-fit terminal 1 is inserted into the through-hole 3 of the substrate 2, the press-fit terminal 1 has a width of the connecting portion 13 (hereinafter also referred to as a terminal width). 3 is formed to be larger than the diameter (A ₀ ± Δ _A ) of FIG. 3, so that the terminal width is reduced and inserted into the through hole 3 in a press-fit state. Contact and connect electrically. The load applied to the press-fit terminal 1 and the substrate 2 at this time is represented by a graph as shown in FIG.

  In the graph of FIG. 2, the vertical axis is the reaction force (compression force or tensile force), and the horizontal axis is the length (terminal width or through-hole diameter). In FIG. 2, P is a curve indicating the load characteristic of the terminal, and Q is a curve indicating the load characteristic of the substrate. When the press-fit terminal 1 is press-fitted into the through hole 3, as shown in the curve P of the load characteristic of the terminal in FIG. Become. Further, the tensile force applied to the periphery of the through hole 3 of the substrate 2 increases in length as the diameter of the through hole 2 increases as the press-fit terminal 1 is press-fitted as shown in the curve Q of the load characteristic of the substrate in FIG. As the length increases, the tensile force increases.

  In the graph of FIG. 2, a point C where the curve P indicating the load characteristic of the terminal and the curve Q indicating the load characteristic of the substrate intersect is a state where the press-fit terminal 1 has been press-fitted into the through hole 3. The reaction force at point C is the contact load x (unit: N). In order to obtain a stable connection structure between the press-fit terminal 1 and the substrate 2 in the long term, this contact load x is the minimum that can provide a low and stable contact resistance, and a maximum that can provide a stable substrate insulation performance. What is necessary is just to set the relationship between the press fit terminal 1 and the board | substrate 2 so that it may enter between contact loads. Hereinafter, the minimum contact load and the maximum contact load will be described.

  The minimum contact load is set to the minimum contact load within a range where stable contact resistance can be maintained in anticipation of an increase in insulation resistance over time. The connection between the press-fit terminal 1 and the through-hole 3 increases the insulation resistance due to a decrease in contact load due to a change with time, and a stable electrical connection state cannot be maintained. For example, when the connection substrate is left in a high temperature state for a long time, oxidation proceeds, stress relaxation of the terminals and the substrate occurs, and the contact load decreases. Also, when the connection substrate is subjected to a temperature cycle in which the atmosphere of the connection substrate is repeated from a low temperature state to a normal temperature or a high temperature state, thermal expansion and contraction occur in the terminal and the substrate, and the contact load decreases due to the influence of oxidation or sliding.

  The graph of FIG. 3 is a graph showing the relationship between the contact load and the contact resistance when the press-fit terminal is press-fitted into the through hole of the substrate, the horizontal axis is the contact load, and the vertical axis is the contact resistance. The initial curve in Fig. 3 shows the initial contact resistance when press-fit terminals are press-fitted into the through hole, and the curve after endurance shows the contact resistance after performing a high temperature storage test and a temperature cycle test as an endurance test assuming in-vehicle use. It is shown. As shown in FIG. 3, when the contact load decreases and becomes a certain value or less, the contact resistance rapidly increases. In addition, as shown by the curve after the durability test, after a lapse of time, the contact load at which the contact resistance rapidly increases further shifts to become smaller.

  In the graph shown in FIG. 3, the initial contact load may be set so as to be used in a region where the contact resistance after the durability test is low and stable. That is, the minimum contact load means that the minimum contact load may be set in a range where a low contact resistance can be maintained in a stable state in anticipation of an increase in contact resistance after durability. In the present invention, the minimum contact load means an initial contact load.

  Hereinafter, the example which calculated | required the minimum contact load concretely is shown. 4A to 4C show the results of measuring the initial contact resistance and the contact resistance after the endurance test by inserting press-fit terminals of various shapes into the through holes of the substrate. The shape of the press-fit terminal is shown, the measurement result of the initial contact resistance is shown in the middle stage, and the contact resistance after the durability test is shown in the lower stage. 4A is an N-type terminal having a cross-section of the connection portion 13 of the press-fit terminal 1, FIG. 4B is an N-type terminal in which the cross-section of the connection portion 13 is partially penetrated, and FIG. The cross section of the part 13 is a needle eye type terminal. Looking at the contact resistance after the durability test of FIGS. 4A to 4C, the contact resistance increases rapidly from the initial contact load of about 35 N. From this result, it can be seen that the initial contact load at which a low and stable contact resistance is obtained even after the durability test is about 35 N regardless of the shape of the press-fit terminal. Therefore, if the minimum contact load is set to 40 N with a margin, it is clear that a stable contact resistance can be obtained even after a long period of time has passed after the terminal press-fitting. In the tests shown in FIGS. 4A to 4C, Sn plating was applied to either the press-fit terminal or the substrate.

  The maximum contact load is set to the maximum contact load within a range in which stable insulation performance can be maintained even if the substrate is whitened over time. It is considered that the decrease in insulation performance is caused by whitening of the substrate due to an impact at the time of press-fitting a press-fit terminal. The substrate 2 is generally a laminate in which an epoxy resin impregnated cloth or the like is stacked on a glass base material. By press-fitting a terminal into the through hole 3 of the substrate 2, the glass cloth and the epoxy resin may be peeled off or the epoxy resin layer may be cracked to cause whitening. When whitening occurs, moisture enters from the gaps caused by cracks and the insulation distance is shortened, resulting in a decrease in insulation performance, and an electric circuit is formed by ionic conduction, resulting in a short circuit with an adjacent terminal. And it is thought that the whitening length of a board | substrate becomes long, so that the contact load with respect to the through hole of a press fit terminal becomes large. Therefore, if the maximum value of the contact load is set within the allowable whitening length range, the insulation performance should not be affected.

  By the way, the whitening of the substrate is not only due to the stress at the time of press-fitting the press-fit terminal. For example, when a through hole is formed by cutting a substrate with a drill, the substrate may be broken and whitened by the impact of the drill. It is extremely difficult to determine whether the whitening of the substrate is present on the substrate itself or by press-fitting a press-fit terminal. However, as shown in FIG. 5, even if whitening 5 occurs by press-fitting the press-fit terminal 1 into the substrate 2, the whitening length is an insulation distance necessary for obtaining sufficient insulation characteristics (necessary insulation distance). ) If it is within the range of B, the insulating performance of the substrate can be sufficiently maintained. That is, even if the substrate is whitened by press-fitting a press-fit terminal, the upper limit of the contact load may be set so that the whitening length is within an allowable range in which the insulation performance can be maintained. As shown in FIG. 5, the necessary insulation distance B is the length from the whitening end B1 to the whitening end B2 of the adjacent terminal. Further, when a conductive layer is provided between through holes as an inner layer, the same idea can be developed for the length up to that.

Assuming that the limit whitening length allowable to be within the range of the necessary insulation distance B is the whitening allowable distance y (unit: mm), the whitening allowable distance y can be expressed by the following equation (2).
(Equation 1)
_{y ≦ <(Z 0 ± Δ} Z) MIN - {(A 0 ± Δ A) MAX +2 (T 0 ± Δ T) MAX + B}> / 2 ··· (2)
As shown in FIG. 1 (a), in the above equation (2), (Z ₀ ± Δ _Z ) _MIN is the pitch between the electrodes (minimum), (A ₀ ± Δ _A ) _MAX is the through-hole diameter (maximum), (T ₀ ± Δ _T ) _MAX is the wall thickness (maximum) of the through hole, and Δ _Z , Δ _A , Δ _T are tolerances of each. The wall thickness of the through hole is the thickness of the conductive layer 4 inside the through hole 3.

here,
(Equation 2)
Z≡ (Z ₀ ± Δ _Z ) _MIN = Z ₀ −Δ _Z
(Equation 3)
A≡ (A ₀ ± Δ _A ) _MAX = A ₀ + Δ _A
(Equation 4)
T≡ (T ₀ ± Δ _T ) _MAX = T ₀ + Δ _T
Then, the above equation (2) can be expressed as the following equation (3).
(Equation 5)
y ≦ {Z− (A + 2T + B)} / 2 (3)
Even if the substrate is whitened when a press-fit terminal is press-fitted into the through hole, the insulation performance can be maintained as long as it is less than the allowable whitening distance y obtained by the above equation (3).

Hereinafter, the example which calculated | required the required insulation distance B concretely is shown. When the relationship between the whitening length of a single substrate and the through-hole diameter of a general vehicle-mounted substrate was examined, it was about 0.2 mm at the maximum as shown in FIG. In addition, the insulation distance of the substrate was changed, and a test was conducted on the deterioration of the insulation resistance between the terminal and the wiring after the high temperature and high humidity test. As shown in FIG. 7, for the insulation resistance between the conductive layer 4 and the wiring pattern 6 in the through hole 3 of the substrate 2, a test piece was prepared in which the insulation distance was changed between 0.2 and 0.4 mm. The insulation resistance after the initial test and after the high temperature and high humidity test was measured. As a result, as shown in FIG. 8, it was found that the insulation resistance was 10 ⁹ Ω, which is the target value, even under the condition of the shortest insulation distance of 0.2 mm, and that the insulation performance was sufficient. The same results were obtained after the high temperature and high humidity test, and there was almost no difference from the initial stage. From this result, it was found that the insulation performance can be sufficiently secured if the insulation distance is 0.2 mm or more. Therefore, the necessary insulation distance B was set to 0.2 mm.

  The actual required insulation distance B of the substrate is considered to be less than 0.2 mm, but it is meaningless because it is impossible to industrially mass-produce a substrate having an insulation distance of less than 0.2 mm. However, the above results are for a general vehicle-mounted substrate, and the value of the required insulation distance B may vary depending on the type (quality) of the substrate. It is desirable that the required insulation distance is determined by measuring the insulation resistance by the above method according to the type of the substrate.

Here, the allowable whitening distance y is calculated using the above-described necessary insulation distance B = 0.2 mm. If the inter-electrode pitch (minimum) Z of the substrate shown in FIG. 1A is 2.2 mm and the through-hole diameter (maximum) A is 1.9 mm, these numerical values are substituted into the above equation (3). ,
Whitening allowable distance y = {2.2− (1.09 + 0.2)} / 2 = 0.455 [mm].

Next, the example which calculated | required the contact load corresponding to whitening allowable distance is shown. First, the relationship between the whitening length and the contact load was examined for various shapes of terminals by a cross-sectional observation technique. The results are shown in the graph of FIG. A straight line R obtained by connecting the maximum whitening length corresponding to the contact load at each point shown in FIG. 9 indicates the relationship between the whitening length S [mm] and the contact load x [N]. Is expressed as the following equation (4).
(Equation 6)
x = 290S + 20 (4)

Here, the maximum allowable whitening length S is the allowable whitening distance y expressed by the above equation (3). Therefore, the maximum contact load that is the upper limit of the contact load can be expressed by the following equation (5). it can.
(Equation 7)
x ≦ 290 {[Z− (A + 2T + B)] / 2} +20 (5)

  From the above, the necessary contact load x that the press-fit terminal should have is a minimum contact load of 40 N or more regardless of the type of the substrate, and the maximum contact load is <290 {[Z- (A + 2T + B)] / 2} +20. It can be seen that it may be set so that it is N or less.

  For example, when the allowable whitening distance y is 0.455 mm, the maximum contact load is about 161 N when y is substituted into {[Z− (A + 2T + B)] / 2} in the above formula (5). As described above, in the straight line R shown in FIG. 9, the contact load at the point corresponding to the whitening length that is the allowable whitening distance can be set as the maximum contact load.

  In order to form the press-fit terminal so as to have the above-described contact load, the contact load can be changed by changing the shape of the connecting portion 13 of the press-fit terminal, the material of the terminal, or the like. The press-fit terminal can be formed by punching a metal wire having excellent conductivity such as a copper alloy into a predetermined shape. In the punching process, the whole is formed to have a uniform thickness, but it is also possible to change the thickness partially by processing the necessary part. Examples of the processing method for changing the thickness of the terminal include press processing and plating. Further, although not particularly shown, plating such as Sn plating can be applied to the entire press-fit terminal 1 or the surface of a portion of the connecting portion 13 that contacts the through hole 3.

  When manufacturing a new press-fit terminal, if it is manufactured so that the contact load of the terminal is within the range of the maximum contact load and the minimum contact load, the long-term stable performance can be surely exhibited. In addition, a press-fit terminal with more stable performance can be obtained by manufacturing the contact load so that the contact load has a certain margin from the limit value, instead of manufacturing the contact load at the limit value within the above range.

  Further, without actually making a prototype of a press-fit terminal, the shape of the terminal can be determined by predicting the performance of the press-fit terminal by simulation using a computer with respect to the shape and contact load of the terminal. As a result, it is possible to rapidly manufacture a new press-fit terminal as compared with the conventional method in which a new press-fit terminal is manufactured by actually repeating trial manufacture and performance evaluation of the terminal.

  The connection structure of the press-fit terminal and the substrate having a through hole according to the present invention can be used as a connection structure of various control boards. When used for connection between electric wire substrates in the electric wiring used, it can be optimally used as a connection structure having high reliability over a long period of time even under severe conditions.

The press fit terminal and board | substrate connection structure of this invention are shown, (a) is explanatory drawing which shows the state before a connection, (b) is explanatory drawing which shows the state after a connection. It is for demonstrating the connection principle of a press fit terminal and a board | substrate, and is a graph which shows the relationship between a compressive force and terminal width, and the relationship between a tensile force and a through-hole diameter. It is a graph which shows the relationship between the contact load after press-fitting a press fit terminal into the through hole of a board | substrate, and contact resistance. (A) to (c) are graphs showing the relationship between the initial contact resistance and the contact load after press-fit terminals of various shapes are press-fitted into the through-holes of the substrate, and after the durability test. It is a graph which shows the relationship between contact resistance and contact load. It is explanatory drawing which shows the cross section of the board | substrate and pressfit terminal for demonstrating the whitening and insulation distance of a board | substrate. It is a graph which shows the result of having investigated the relationship between the whitening length of a board | substrate, and the through-hole diameter. It is explanatory drawing which shows the measuring method of the insulation resistance of the wiring of a board | substrate, and a terminal. It is a graph which shows the measurement result of the insulation resistance after the initial stage of the board | substrate which changed the insulation distance, and a high temperature / humidity test. It is a relationship between the contact load of the terminal and the whitening length.

Explanation of symbols

1 Press-fit terminal 2 Substrate 3 Through hole 4 Conductive layer

Claims (2)

In the connection structure between a press-fit terminal and a board in which a press-fit terminal is inserted into the through hole of the board in a press-fitted state, the contact load x [N] when the press-fit terminal is inserted into the through hole is expressed by the following equation (1). A press-fit terminal and substrate connection structure, wherein the press-fit terminal and the substrate are formed so as to be within the range shown.
40 ≦ x ≦ 290 {[Z− (A + 2T + B)] / 2} +20 (1)
In the above equation (1), Z [mm] is the pitch between the through holes (minimum), A [mm] is the through hole diameter (maximum), T [mm] is the through hole wall thickness (maximum), and B [ mm] is the minimum necessary insulation distance necessary to ensure insulation between the terminal and the wiring. In the method of designing a press-fit terminal that is inserted into a through-hole of a board in a press-fit state, an initial contact load that provides stable contact resistance after a press-fit terminal is press-fitted into the through-hole of the board and a durability test is performed Set as the minimum contact load, as the insulation distance between the wiring pattern of the board and the through-hole, obtain the required insulation distance that provides stable insulation resistance after the high-temperature and high-humidity test of the board. Obtain the distance, press-fit multiple press-fit terminals with different contact loads into the through-holes of the board, measure the whitening length of the board, find the relationship between the whitening length and the contact load, and based on this relationship the whitening allowable distance Is set as the maximum contact load, and the contact load of the press-fit terminal is not less than the minimum contact load and the maximum contact So that heavy below, the design method of a press-fit terminal, characterized by designing the press-fit terminal.

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