JP2015090332A - Life prediction structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of accurately predicting a life of a solder by mounting a mechanism on a board for predicting that a solder connected portion of a mounted component connected to a circuit board comes to the end of a creep rupture life by an electrical scheme for breaking of a wire before the component connected portion.SOLUTION: Provided is a life prediction structure including a non-horizontal circuit board in a housing, metal singulated pieces 2 being soldered to two lands 11 connected to a breaking-of-wire detection circuit 12 formed on the circuit board with a small gap between the pieces 2.

Description

  The present invention relates to a life prediction structure.

  For the connection between the electronic component and the circuit board, for example, Sn-37Pb (unit: mass%) that can be soldered at around 220 ° C., or lead-free solder alloy Sn-3Ag-0.5Cu (unit: lead) that does not use lead. Mass%) is used.

  At present, low silver solder with low material cost is attracting attention in both insertion and surface mounting using lead-free solder, and together with the current Sn-3Ag-0.5Cu, etc., electronic components are mounted with various solders. ing.

  As a result, there is a situation where it is difficult to predict the life of the same component used under various conditions (board specifications / environment).

  On the other hand, Patent Document 1 discloses a method for predicting the lifetime by measuring the temperature of the substrate.

JP2011-253971

  The technique disclosed in Patent Document 1 has a problem that a special circuit for measuring the temperature is required and the cost is increased. In addition, since it is a method of estimating the lifetime based on the temperature, it is inevitable that the accuracy will fluctuate.

  A life prediction structure comprising a conductive member that connects two connecting portions provided on a substrate, and the life is determined by detaching the conductive member from at least one of the connecting portions.

  According to the present invention, it is possible to perform reliable life prediction according to the actual specification state.

  Further means and effects of the present invention will be apparent from the following description.

It is explanatory drawing in connection with a 1st Example. It is explanatory drawing in connection with a 2nd Example. It is explanatory drawing in connection with a 3rd Example.

  Hereinafter, the contents of the present invention will be described in detail using examples.

  FIG. 1 shows a structure in which two disconnection detection lands (connection portions) 11 are provided on a circuit board 1 and the two are electrically connected to a metal piece 2. This conductive connection is made by solder. The two disconnection detection lands are connected to a disconnection detection circuit 12 that discriminates the conduction and insulation states between the disconnection detection lands.

  When the circuit board 1 is installed at an angle, for example, perpendicular to the housing, a drop force acts on the metal piece 2 due to its own weight. When the connection structure using solder reaches the end of its life, the connection between at least one of the disconnection detection lands and the metal piece is stopped. In particular, when both connections reach the end of their lives, the metal piece itself falls off and the disconnection detection circuit detects the insulation state. This makes it possible to accurately measure the life of the solder in the actual usage state.

  In other words, if the board is fixed vertically or diagonally, or if the circuit board may temporarily stand vertically or tilt diagonally depending on the usage environment, connect to this board. The mechanism that predicts the creep rupture life of soldered joints of mounted parts by using electrical methods prior to the connection of parts will not interfere with the increase in mounting density, At the same time as the soldering using the process, it can be mounted on the circuit board.

  As one of the methods, a mechanism that predicts the creep rupture life of the solder connection portion of the mounted component connected to the circuit board by an electrical method by disconnecting the component connection portion before the component connection portion is provided on the substrate. How to implement.

In that case, it is desirable that a stress larger than the maximum stress applied to the mounting component connecting portion by solder is constantly applied, and an electrical disconnection can be created by creep rupture before the mounting component connecting portion.
At this time, a large mounting area is not required so that high mounting density is not hindered, and strict precision of dimensional accuracy is not required. It is desirable to simultaneously create a process (reflow / flow) and not increase the number of production steps, and the structure of this embodiment can satisfy these requirements simultaneously.

  In other words, since the metal piece as a lifetime prediction mechanism has potential energy, this energy can be used as a driving force for disconnection.

  Therefore, as shown in FIG. 1, two or more disconnection detection lands 11 formed with a narrow gap on the circuit board 1 are connected to the end portions of the elongated metal pieces 2 such as copper that can be soldered simultaneously with other components. The circuit board 1 is fixed vertically or obliquely to the housing by reflow connection so that the metal pieces 2 are arranged in the horizontal direction as much as possible.

  The two or more disconnection detection land connection portions formed by the above method can be used as a mechanism for easily detecting a breakage by easily creating a large constant load by stress multiplication based on the lever principle.

  Specifically, this prediction mechanism is made of a metal piece that is easily wetted by solder such as copper, and is mounted on a circuit board at the same time as other surface-mounted components.

  In addition, on the mounting surface of the metal piece 2 on the circuit board 1, where solder does not need to be wetted, if solder resist is applied, solder connection is stably performed only in places other than the applied, It is possible to reduce the variation in the connection area with the circuit board 1 and to improve the accuracy of connection life prediction.

  Furthermore, the positions of the electrodes to be connected to the circuit board 1 are separated from each other within the mounting surface of the metal piece 2, thereby reducing the effect of stress multiplication by the above-described lever principle. Therefore, if the metal pieces 2 are formed as close as possible to each other, or the metal pieces 2 are made as long and narrow as possible, and the longitudinal direction thereof is arranged as horizontally as possible, the mechanism can be realized by using a small volume of metal. It is possible to reduce the space to be used.

  It is necessary to form an electrode having the same shape as that of the prediction mechanism as the electrode shape on the circuit board 1 side. In addition, it is necessary to connect the electrode on the circuit board side to the disconnection detection circuit 12 by surface wiring so as to electrically detect disconnection that occurs when the metal piece falls due to creep deformation of the solder material used for connection. is there.

  As an example, the circuit board is vertically placed, and a large QFP, a surface mount type transformer, and a coil are mounted. Further, a prediction mechanism of a type that is broken by gravity is soldered. This prediction mechanism is made of rectangular parallelepiped copper, and the dimensions of the mounting surface on the circuit board are 37 mm long, 6 mm wide, and 3 mm thick. In addition, a solder resist is applied on the mounting surface on the circuit board so that the solder does not get wet, leaving two rectangular areas of 1 mm in length and 0.5 mm in width to be electrodes.

  Further, each of the two electrodes is formed in the vicinity of a diagonal position on the mounting surface (length: 37 mm, width: 6 mm).

  The electrode on the circuit board side is also formed with the same shape as that of the prediction mechanism, and is connected to the disconnection detection circuit.

  This circuit board was placed in a high-temperature thermostatic chamber at 100 ° C., and a creep life acceleration test was performed with the disconnection detection circuit turned on.

  As a result, it was found that the connection part of the rectangular parallelepiped copper was broken in 80% of the time for the surface-mounted coil to be creep-broken, and the prediction mechanism was established.

  The present embodiment is an example in which a prediction mechanism is formed using energy other than potential energy.

  As shown in FIG. 2, a prediction mechanism using an elastic body 3 such as a leaf spring connected to two or more disconnection detection lands 11 formed with a narrow gap on a circuit board 1 and using potential energy generated by the spring force. Can be built.

Specifically, as a mechanism for accumulating potential energy due to the spring force, a mechanism is proposed in which an elastic stainless steel plate is folded in half and U-shaped by deformation within an elastic range.
However, it is necessary that a rectangular electrode is formed at each of the folded ends for connection to the circuit board.

  Similarly in this case, it is necessary to form an electrode having the same shape as that of the prediction mechanism as the electrode shape on the circuit board 1 side. In addition, the electrode on the circuit board 1 side must be coupled to the disconnection detection circuit 12 by surface wiring so that the disconnection that occurs when the metal piece falls due to creep deformation of the solder material used for connection must be detected. There is.

  An example of the configuration of this embodiment is as follows.

  The circuit board is vertically placed, and a large QFP, a surface mount type transformer, and a coil are mounted thereon. Furthermore, a prediction mechanism of a type that is disconnected by a spring force is soldered.

  This prediction mechanism has a U-shape in which a 0.2 mm-thick stainless steel plate is folded in half, and its dimensions are 30 mm in length, 2 mm in width (distance where the folded-up tip faces each other), and 3 mm in height. The curvature radius of the U-shaped part is 1 mm. However, a rectangular electrode having a length of 1 mm and a width of 0.5 mm is formed at each of the folded ends, and these become mounting portions on the circuit board.

  The electrode on the circuit board side is also formed with the same shape as that of the prediction mechanism, and is connected to the disconnection detection circuit.

  This circuit board was placed in a high-temperature thermostatic chamber at 100 ° C., and a creep life acceleration test was performed with the disconnection detection circuit turned on.

  As a result, it was found that the connection part of the rectangular parallelepiped copper was broken in 80% of the time for the surface-mounted coil to be creep-broken, and the prediction mechanism was established.

  As a method of accumulating potential energy in the spring, there is a method of using an external force applied to a circuit board during product production.

  One example is the use of a force for pushing the circuit board when the circuit board is attached to the product housing.

  As shown in FIG. 3, the prediction mechanism in this case is preferably a V-shape obtained by folding a metal plate having elasticity into two, and two or more electrodes are formed at a position close to the tip of one side folded in two. The plate spring is used as the elastic body 3, and these electrodes are used as mounting parts on the circuit board.

  Further, an electrode having the same shape as that of the prediction mechanism is formed on the circuit board 1 side, and is connected to the disconnection detection circuit 12.

  The other tip that is folded in two is out of the circuit board, and when the board is slid into the product housing 50 and inserted, the tip is pushed back to the board.

  With this force that is pushed back, the potential energy of the spring force can be accumulated in the metal plate.

  The configuration in this example is shown below.

  The circuit board is vertically placed, and a large QFP, a surface mount type transformer, and a coil are mounted thereon. Furthermore, a prediction mechanism of a type that is disconnected by a spring force is soldered.

  This prediction mechanism has a V-shape formed by folding a 0.2 mm-thick stainless steel plate in half, and the dimensions are 50 mm for the length of one side of the V-shape and 2 mm for the width (distance where the tip of the half-fold faces each other) Thus, the height is 3 mm and the radius of curvature of the bent portion is 1 mm. However, a rectangular electrode having a length of 1 mm and a width of 0.5 mm is formed at a position of 2 mm and 4 mm from the tip of one side which is folded in half, and these become mounting portions on the circuit board.

  The electrode on the circuit board side is also formed with the same shape as that of the prediction mechanism, and is connected to the disconnection detection circuit.

  Another tip that is folded in two is 2 mm outside the circuit board, and when the board is slid into the housing and inserted, the tip is pushed back to the circuit board.

  This substrate was placed in a high-temperature thermostatic chamber at 100 ° C., and a creep life acceleration test was performed with the disconnection detection circuit turned on.

  As a result, it was found that the connection part of the rectangular parallelepiped copper was broken in 80% of the time for the surface-mounted coil to be creep-broken, and the prediction mechanism was established.

  The embodiments described above may be used in combination with the idea.

  The center of gravity of the two or more lands formed on the substrate may be different from the center of gravity of the metal piece on the soldering surface.

  As described above in detail, by applying the life prediction mechanism of the present invention, it is possible to predict the life of solder in various electric circuits.

DESCRIPTION OF SYMBOLS 1 ... Circuit board 11 ... Disconnection detection land 12 ... Disconnection detection circuit 2 ... Metal piece 3 ... Elastic body 50 ... Product housing

Claims (6)

  Life prediction, characterized in that a metal piece is soldered to two lands connected to a disconnection detection circuit, which has a non-horizontal circuit board in the housing and is formed with a narrow gap on the board. Construction   2. The life prediction structure according to claim 1, wherein the center of gravity of the two or more lands formed on the substrate is different from the center of gravity of the metal piece in the soldering surface.   3. The life prediction structure according to claim 2, wherein the metal pieces are elongated and attached to the substrate substantially horizontally so as to be different from the center of gravity.   2. The life prediction structure according to claim 1, wherein a conductive elastic body storing potential energy due to a spring force is soldered between two or more lands formed on the substrate.   5. The life prediction structure according to claim 4, wherein the conductive elasticity is a letter or V-shaped leaf spring.   The conductive elastic body is a U-shaped or V-shaped leaf spring, and an electrode connected to the substrate is provided at one end thereof, and the other end protrudes from the substrate, or the outside of the substrate. 5. The life predicting structure according to claim 4, wherein the leaf spring can accumulate potential energy by an operation at the time of mounting the substrate to the product by being arranged at a position where the external force from can be received.

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