Patent Application
20080142571
The present application claims priority from Japanese application JP2006-327296 filed on Dec. 4, 2006, the content of which is hereby incorporated by reference into this application.
1. Field of the Invention
The present invention relates to an electronic device as typified by a motor driver unit, a direct injection engine control unit, etc. for automobiles.
2. Description of the Related Art
In consideration of environmental problems, it is expected that automobiles driven by an electric motor as typified by a hybrid car will become more widely used in the future. Further, there is a strong trend toward replacing a power steering and a brake hydraulically controlled conventionally with an electronic control unit (ECU) utilizing an electric motor. A motor control ECU uses IGBT and FET chips having a large current flow and therefore generates heat of several tens to hundreds of watts. The generated heat needs to be cooled with water cooling or air cooling. Further, although it is thought that the demand for a direct injection engine control unit will increase in the future, it is necessary to treat a comparatively large current in terms of the function thereof. Each of these ECUs includes a section with a large current flow exhibiting a high heat release value, requiring enhanced heat dissipation properties, and a section with a small current flow exhibiting a low heat release value, not requiring enhanced heat dissipation properties. With many products, it is structurally advantageous to manufacture these sections as separate circuits, i.e., the former as a power module and the latter as a control module, and configure these circuits on two different substrates. For connection between the two substrates, a technique for connecting between terminal pads thereof by use of a lead frame connector can be used. In this case, solder or ultrasonic joining is mainly used to connect the lead frame connector and the pads.
The shape of a conventional lead frame connector 101 is as shown in
JP-A-2006-179312 discloses a connector pin for a camera module, which is bifurcated to be used for each of conduction with the module bottom and an external terminal, and a bifurcated pin joint is arranged only on one side in order to downsize the connector.
Solder joining between a lead frame connector and a module is restricted in terms of many aspects of process. For example, on the premise of joining between substrates, mounting of components on each substrate is completed and therefore many components have already been mounted on the substrate by soldering. Therefore, to joint a module with a lead frame connector, it is common to take measures for partially melting solder through local heating, etc. so that a soldered joint of a mounted component does not re-melt. Therefore, if joining is performed only on one side, the joining force is weak and a soldered section of a mounted component may re-melt resulting in removal of the component and connection failure.
Further, a method of ultrasonically joining the lead frame connector and the pad has been proposed as a joining method without using solder. In the case of a ceramic substrate such as LTCC and SiC, the power of the ultrasonic wave is efficiently transmitted to the joint because of sufficient rigidity thereof, making it possible to sufficiently increase the joining strength. However, there arises a problem that the cost also increases. In order to solve this problem, a metal base substrate using resin for an insulating layer may be used. In this case, however, the insulating resin layer included in the metal base substrate absorbs the power of the ultrasonic wave, decreasing the joining strength. Therefore, sufficient joining strength cannot be obtained if joining is performed only on one side.
If a joint is formed only on one side with respect to the body as shown in
In order to solve the above-mentioned subject, an electronic device according to an aspect of the present invention comprises: a first substrate having first components mounted thereon; a second substrate having second components mounted thereon; and a lead frame connector which connects the first and second substrates, the connector having a body, a first joint at one end of the body, and a second joint at the other end of the body, the first joint being formed such that two joint pieces mutually protrude in opposite directions substantially perpendicularly to the one end of the body at a boundary position between the body and the first joint; wherein the first joint of the lead frame connector is joined with electrode pads provided on the first substrate, and the second joint of the lead frame connector is joined with an electrode pad provided on the second substrate, thereby connecting the first and second substrates.
Further, the electronic device according to another aspect of the present invention comprises: a first substrate having first components mounted thereon; a second substrate having second components mounted thereon; and a lead frame connector which connects the first and second substrates, one end of the lead frame connector being formed in the T shape; wherein the T-shaped one end is joined with electrode pads provided on the first substrate, and the other end is joined with an electrode pad provided on the second substrate, thereby connecting the first and second substrates by means of the lead frame connector;
Preferably, the first component is a high heat generation component and the second component is a low heat generation component.
Preferably, the first and second substrates are arranged so that the component-mounted sides thereof face each other.
Preferably, the first substrate is a metal base substrate and the second substrate a resin substrate.
Preferably, the first joint is split into a plurality of joint pieces.
Preferably, each joint piece of the first joint of the lead frame connector and the electrode pad are ultrasonically joined with an aluminum foil sandwiched therebetween.
Preferably, both the lead frame connector and the electrode pad are made of copper.
In accordance with the present invention, there can be provided an electronic device having sufficient reliability on lead connection, and particularly an electronic device having sufficient joining strength without damaging the resin even when the lead frame connector is ultrasonically joined with a substrate using resin such as a metal base substrate.
Preferred embodiments for carrying out the present invention will be described below.
An embodiment which can realize an ECU adapted to provide sufficient reliability for use in a motor driver unit or a direct injection engine control unit for automobiles will be explained below. First, a general structure of the ECU is shown in
Normally, circuits having a comparatively large current flow and high heat generation components are mounted on the power module. Since the power module requires high heat dissipation properties, a ceramic substrate having high thermal conductivity is normally used. However, a metal base substrate having an insulating resin layer and being capable of improving heat dissipation properties is used from the viewpoint of cost. Aluminum is used as a base metal from the viewpoint of processability and weight. The use of copper makes it possible to further improve heat dissipation properties. Further, since the coefficient of thermal expansion can be equalized with copper wiring, the warp of the substrate can be reduced. A copper foil used for ordinary printed circuit boards can be used as wiring for the substrate. Although unnecessary because of ultrasonic joining, nickel and gold plating may be applied to a pad for solder joining. In this case, although nickel and gold plating is formed also on a pad for ultrasonic joining, no problem occurs as long as joining conditions are appropriately selected.
A perspective view of the lead frame connector 1 (31) in the electronic device of the present invention is shown in
Further, as shown in
In the process of joining with the substrate, for example, the end of an ultrasonic bonder oscillator is pressed on one joint piece at the time of joining, and then the end of the oscillator is pressed on the other joint piece in the same manner at the time of joining. If the end shape of the oscillator is devised as shown in
With a resin base substrate, if the power of the ultrasonic wave is too intensive, damage is concentrated on the insulating resin layer having the lowest strength, which may cause the resin to get burned or destroyed resulting in exfoliation of wiring from the resin. Therefore, joining needs to be performed with weak power. The present invention, wherein an area per joint piece between the lead frame connector and the substrate is reduced but joining is performed at a plurality of positions, is advantageous as a method of sufficiently maintaining the joining strength while avoiding damage to the substrate.
Further, the present invention makes it possible to use a small joint area not only with a metal substrate but also with an ordinary resin substrate (printed circuit board), which is very effective to improve the mounting density. Although the use of a resin substrate for the power module is very difficult in terms of heat dissipation properties, a resin substrate is used for the control module if the control module is arranged within the same housing as that of the power module. Further, insulating resin materials having high heat conductivity made of epoxy resin with mixed filler of aluminum or silica have been developed in recent years. Accordingly, it may be possible to use a resin substrate made of such materials for the power module.
Although the power and control modules are arranged so that the component-mounted sides thereof face each other in order to reduce the capacity of the entire modular structure in many cases, it is clear that the same effect is also obtained even if these modules are laterally arranged.
A second embodiment is shown in
While we have shown and described several embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to those skilled in the art, and we therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-327296 | Dec 2006 | JP | national |
