JPH03201554A - Electronic part to be packaged on board - Google Patents

Abstract

PURPOSE:To approximately securely prevent a lead from floating at the time of joint by a method wherein each lead is subjected to thermoelastic martensitic transformation exhibiting a shape memory effect at a temperature higher than room temperature and lower than soldering temperature as well as is formed of shape memory alloy having conductivity. CONSTITUTION:Each lead 3 of a flat package IC 3 is mounted on soldering paste 54 adhered on a pad 53 on a board 51. Even if a lead 32 is deformed and floated upward, the lead which is deformed at the time of heating wherein the lead is passed through a re-flow furnace as a heating means reaches a temperature of martensitic transformation or higher and is restored to an original state before the deformation by a shape memory effect so that contact faces 3b of all leads 3a are positioned on the same plane. At the same time the soldering paste 54 is melted, all the leads 3 are uniformly soldered and after the lead is passed through the re-flow furnace it is cooled to have the solder solidified so that the pad 53 and the lead 3 are electrically (and mechanically) connected to each other.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an electronic component for mounting on a board, and more specifically, the present invention relates to an electronic component for mounting on a board, and more specifically, to solder on a conductor-forming surface of a printed wiring board made of an insulating material such as a ceramic or an organic material. The appendix relates to electronic components for board mounting that are mounted by et al.

[Background technology]

In recent years, consumer devices have become smaller, thinner, and lighter.
``Requirements for miniaturization and automatic assembly of electronic components are increasing. Under such circumstances, flat package IC
In most cases, electronic components such as electronic components are mounted on printed wiring boards as part of automatic assembly.

The process of mounting a conventional flat package IC or the like onto a printed wiring board is performed as follows.

That is, as shown in FIG. 5, ceramic.

Several conductor patterns 52.52. are formed in advance on the surface of the printed wiring board 51 made of an insulating material such as an organic material.・
Solder pads (hereinafter referred to as ``pads'') 53, 53, . In this FIG. 5, ten conductor patterns 52 are provided,
A pad 53 is shown at the tip of each conductive pattern 52, respectively.

Then, there are ten external terminals (hereinafter referred to as "leads") 41 corresponding to the pads 53, specifically five external terminals (hereinafter referred to as "leads") led out in two directions. ．． An electronic component 40 such as a flat package IC having an angle of 41□, . (not shown), the solder is reflowed (remelted), cooled and solidified to achieve bonding and conduction.

However, according to this method, if there is a lead that has been lifted up due to deformation, such as lead 4h shown in FIG. 5, the lead may remain lifted and not be properly joined as shown in FIG. was difficult and caused problems later on.

In order to solve these problems, several proposals have been made as shown below.

■Preliminary shaping of stress concentration points by providing notches, etc. in parts other than the tip of each lead of the electronic component, making the tip of each lead face the board at an acute angle, and placing the electronic component on the solder pad. iS! After placing the electronic component on the board, the main body of the electronic component is pressed toward the board, causing plastic deformation at the stress concentration area and bringing the tip of the lead into contact with the solder pad, thereby reflowing the solder. For example, JP-A-59-178
There are issues such as No. 790.

■A frame-shaped glass is formed on the leads of electronic components placed on the conductor pattern of the board via solder paste etc. so that it can come into contact with all the leads, and a frame-shaped glass is fixed on the outer edge of this glass. A special holding tool made of a magnetic material is placed on the board, and a magnet placed under the board attracts the magnetic material to bring the leads into contact with the conductor pattern, and the radiant energy is applied while looking through the connection parts of the leads. A method of irradiating a beam (YAG laser, etc.) through glass, etc. to melt solder, etc.

For example, there is Japanese Patent Application Laid-Open No. 59-217388.

■A method in which the tip of an electronic component lead is shaped into a shape that can be embedded in solder paste, the tip is embedded in the solder paste at a predetermined speed, and then the solder is reflowed.

For example, there is Japanese Patent Application Laid-Open No. 60-60795.

■A method in which force is applied from above the electronic component and all leads of the electronic component are soldered while maintaining close contact with the pads on the board. For example, there is Japanese Patent Application Laid-Open No. 62-37992.

[Problem to be solved by the invention]

However, the conventional examples shown in (1) and (3) have the following disadvantages. That is, as shown in FIG. 7, an electronic component 40 such as a flat package IC usually has a semiconductor element 30 molded with a synthetic resin 31 such as epoxy or silicone, and leads 4 in two directions (or four directions).
1 is drawn out, and the semiconductor element 30 and each lead are connected with bonding wires 42. For this reason,
The mechanical stress generated by the force F during pressing causes breakage of the bonding wire 42 and cracks in the semiconductor element 30, which in turn causes a decrease in reliability.

In addition, the conventional example shown in (■) above requires a special holding tool as described above, and has the essential drawback that it is unsuitable for methods other than radiant energy beam component mounting. There is.

On the other hand, in the method (2) of the conventional example above, it is thought that a decrease in reliability due to mechanical stress during pressing can be prevented, but if the deformation of the lead 41 is large, the solder paste 54 may be melted by heating. However, as shown in FIG. 8, the deformed leads 41 are not soldered to the conductor pattern 52 on the substrate 51, and even this method has the disadvantage that poor bonding cannot be completely prevented.

Incidentally, no matter how precisely the lead of the electronic component is manufactured, the deformation of the lead of the electronic component as described above cannot be completely prevented because it occurs during transportation and handling during transportation.

[Purpose of the invention]

An object of the present invention is to improve the disadvantages of the conventional example, and in particular, to prevent a decrease in reliability due to mechanical stress during mounting, and to solve the problem of soldering during bonding without limiting the method of soldering. It is an object of the present invention to provide an electronic component for mounting on a board, which can substantially reliably prevent lifting of leads.

[Means to solve the problem]

The present invention has an electronic component body formed by molding a semiconductor element with a synthetic resin, and at least four external terminals led out in at least two directions from the electronic component body, and is made of ceramic, organic material, etc. In electronic components for board mounting mounted on wiring boards made of insulating materials such as The shape of each lead before deformation is made of a conductive shape memory alloy, and the contact surface with the conductor portion on the wiring board provided in advance at the tip of each lead is approximately the same. The configuration is such that the shape is located on a plane.

This aims to achieve the above-mentioned purpose.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 1 shows a flat package ICI as an electronic component according to the present invention and a substrate 51 on which this flat package IC1 is mounted.

The flat package ICI includes a package IC main body 2 as an electronic component main body, leads 31.3□ led out in two directions from the package IC main body 2 toward the outside,
......3. It has

Of these, the package IC body 2 includes a semiconductor element (not shown here), similar to the electronic component 40 of the conventional example described above.
and a synthetic resin mold 2 for molding this semiconductor element.
A, and bonding wires (not shown here) that electrically connect the semiconductor element and each lead 3.

Each lead 3 is formed of a conductive shape memory alloy that undergoes thermoelastic martensitic transformation exhibiting a shape memory effect at a temperature higher than room temperature and lower than soldering temperature. Further, each of these leads 3 is formed to have a Z-shaped cross section, and one end thereof is embedded in the synthetic resin mold 2A, and the other end is formed at the tip of a conductive pattern 52 as a conductor portion on the wiring board 51. Bad 53
A contact portion 3A that comes into contact with is formed. The lower surface of each contact portion 3A serves as a contact surface 3b with the conductor portion.

As shown in FIG. 2, the original shape before deformation is such that all the contact surfaces 3b are located on substantially the same plane. In this FIG. 2, reference numeral 10 indicates a virtual plane.

On the other hand, the substrate 51 is made of an insulating material such as ceramic or organic material, and has ten conductor patterns 52 formed on its upper surface in FIG.

A pad 5 is provided at one end of each of the conductive patterns 52.
3 is formed, and a solder paste 54 is adhered thereon.

Next, the flat package ICI according to this embodiment is attached to the substrate 5.
The effects etc. when implemented in 1 will be explained.

First, connect each lead 3 of the flat package ICI to the board 5.
It is placed on the solder paste 54 that is adhered to the pad 53 on the top of the solder paste 54. This state is shown in FIG. As shown in FIG. 3, even if the lead 3□ is deformed and floating upwards, similar to the lead 41t shown in FIG. 4. The deformation occurs when the material is passed through and heated. reaches the martensitic transformation temperature or higher and returns to its original state before deformation due to the shape memory effect (see FIG. 4), so that the abutment surfaces 3b of all the adhesives 3 are located on the same plane. At the same time, the solder paste 54 is also melted, and all the leads 3 are evenly soldered. After passing through a reflow oven, the solder is cooled and solidified, and the pads 53 and leads 3 are electrically (
and mechanically).

As explained above, according to this embodiment, each lead 3 returns to its pre-deformation shape due to the shape memory effect during the process of passing through the reflow oven, and the contact surfaces 3b of all the leads 3 are positioned on the same plane. Therefore, even if any of the leads 3 of the flat package ICI are deformed, soldering is performed with the contact surfaces 3b of all the adhesives 3 in close contact with the surface of the pad 53. Soldering can almost completely prevent defects and poor connections. In addition, since the shape memory effect of the shape memory alloy is utilized, there is no need to strongly press the package IC body 2 toward the substrate. The occurrence of crank can be effectively prevented.

Note that the method of mounting electronic components according to the present invention is not limited to the above-mentioned method of soldering, but may also include, for example, using a so-called conductive adhesive instead of a hang paste and using reflow roller as in the above embodiment. It is also possible to make electrical (and mechanical) connections between the leads and the pads.

In addition, a nitrogen gas atmosphere furnace is used for reflow.

Alternatively, a method using high temperature air may be used instead of nitrogen gas. Furthermore, mounting on the substrate using a radiant energy beam such as a YAG laser or a CO□ laser is also possible.

In addition, after temporarily fixing electronic components on the base board with adhesive,
Even in the solder dip method, in which the mounting surface of electronic components is immersed in a heated and molten solder bath, the leads that are deformed during the heating process to assimilate the adhesive or the immersion process in the heated and molten solder bath are not deformed due to the shape memory effect. The present invention can be easily applied. As described above, the present invention can be applied to most methods as long as it can be heated to a temperature higher than the melting point of solder, etc., and thus has wide versatility.

[Effects of the Invention] As explained above, according to the present invention, each lead has a conductive shape that causes a thermoelastic martensitic transformation that exhibits a shape memory effect at a temperature higher than room temperature and lower than soldering temperature. In addition to being made of a memory alloy, the shape of each lead before deformation is such that the contact surfaces with the conductor portion on the substrate provided in advance at the tip of each lead are located on substantially the same plane. Therefore, during heating during the mounting process, each lead returns to its pre-deformation shape due to the shape memory effect, and the contact surfaces of all the leads are positioned on the same plane.

Therefore, soldering is performed with the contact surfaces of all the leads in close contact with the surface of the band, which almost completely prevents soldering defects and connection failures caused by lifting of the leads, and also improves the shape. Since the memory effect is used, there is no need to strongly press the electronic component body toward the board, so it is possible to prevent a decrease in reliability caused by mechanical stress during pressing. Since all that is required is heating, it is possible to provide an electronic component for board mounting that has unprecedented versatility and can be applied to any soldering method.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view showing an electronic component according to an embodiment of the present invention and a board for mounting the electronic component before mounting, and FIG.
The figure is an explanatory diagram showing the shape of the electronic component in Figure 1 before deformation, Figure 3 is an explanatory diagram showing the mounting process of the electronic component in Figure 1, and Figure 4 is an explanatory diagram showing the shape of the electronic component before deformation.
The drawings are explanatory diagrams of operations during the mounting process of the electronic component shown in FIG. 1, and FIGS. 5 to 8 are explanatory diagrams showing conventional examples. 1...Flat package I as an electronic component
C12...Package body as electronic component body, 2A...Synthetic resin mold, 3...
・Lead, 3b...Contact surface, 51...
Wiring board, 52... Conductor pattern as a conductor part.

Claims (1)

[Claims] (1). It has an electronic component body made of a semiconductor element molded with synthetic resin, and at least four external terminals led out in at least two directions from the electronic component body, and is made of an insulating material such as ceramic or organic material. In electronic components for board mounting mounted on a wiring board made of a material, each of the external terminals undergoes thermoelastic martensitic transformation exhibiting a shape memory effect at a temperature higher than room temperature and lower than the soldering temperature, and It is formed from a shape memory alloy that has conductivity, and the shape of each external terminal before deformation is
1. An electronic component for mounting on a board, characterized in that surfaces of the external terminals that come into contact with conductor portions on the wiring board provided in advance at the tips of the external terminals are shaped so that they are located on substantially the same plane.