JPH04181762A - Electronic component - Google Patents

Abstract

PURPOSE:To enhance a heat efficiency at the bonding operation of a lead and to prevent the dislocation and the thermal deterioration of an electronic component by a method wherein the whole region or at least a partial region other than a bonding region which is bonded to other electronic circuit elements on the surface of the lead is covered with a material whose heat radiation coefficient is high. CONSTITUTION:The whole region or at least a partial region other than a bonding region 4a on the surface of a lead 4 is covered with a high-heat- radiation-coefficient layer 5. Thereby, the bonding region 4a of the lead 4 is brought into contact with other electronic circuit elements such as an interconnection pad 7 and the like. When the high-heat-radiation-coefficient layer 5 is irradiated with a laser beam alpha, the laser beam alpha is absorbed efficiently, and the lead 4 can be bonded to the other electronic circuit elements in a short time. Since the lead 4 is covered with the high-heat-radiation-coefficient layer 5, heat is dissipated well immediately after a bonding operation, and the cooling speed of the lead 4 is large. Thereby, a heat efficiency can be enhanced at the bonding operation of the lead, and it is possible to prevent the dislocation and the thermal deterioration of an electronic component.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is applicable to electronic devices such as ICs (integrated circuits) and electronic components that are equipped with leads for bonding to other electronic circuit elements such as wiring pads by a heating method. Regarding parts.

“Background technology” With the trend toward miniaturization of electronic devices, SMT (surface mount technology) and C
Technologies such as OB (chip on board) are being developed. In these electronic components, when joining leads to wiring pads on wiring boards, it is necessary to align them with each other and join them precisely. Conventionally, leads are joined by applying heat and pressure to the leads at the same time. Ta.

However, as the pitch of leads becomes smaller due to higher density component mounting, methods of joining leads using only optical energy such as laser beam irradiation are being considered.

For example, in the case shown in FIG. 8, a bare chip IC 51 is placed on a wiring pad 58 of a wiring board 52 using TAB
Figure 10 shows how the flat package IC 61 is mounted on the wiring board 6.
This figure shows surface mounting on the wiring pad 63 of No. 2. These bare chip IC51 and flat package 61
When mounting electronic components such as
Apply preliminary solder 54.64 to IC 51, 6.
1 on the wiring board 52°62 and position each lead 55.65 on the wiring pad 53.63, as shown in FIGS. 9 and 10.
The laser beam α is irradiated onto the top of ゜65 and scanned, and the lead 55.65 is heated by the laser beam α and the lead 5 is
5.85 and wiring pad 53.63 are soldered.

However, when soldering leads, the surface is usually plated to make the surface glossy in order to improve solder leakage, improve corrosion resistance, and further reduce resistance. . In general, the metals (polished surfaces) used for plating the leads, such as gold, silver, and tin, have poor heat absorption properties due to their low thermal emissivity ε, as shown in Figure 11, and have glossy surfaces. Since the lead reflects light (infrared rays), the heating efficiency is extremely low, making it difficult for the lead to heat up. As a result, in the method of bonding leads using only optical energy, heat is conducted to the IC before sufficient thermal energy is obtained to bond the leads, raising the temperature of the IC and causing thermal deterioration. there were.

Furthermore, during cooling after solder welding, since the heat emissivity of the plating on the surface is low, it takes time to cool and fix, and there is a risk that the REIT may become misaligned during that time. Therefore, when connecting narrow pitch leads to narrow pitch wiring pads,
Misalignment of the leads may cause a short circuit between the leads, which is an obstacle to reducing the pitch between the leads.

The present invention has been made in view of the drawbacks of the conventional examples described above, and its purpose is to improve the thermal efficiency when joining leads by only heating such as laser light, and to improve the thermal efficiency. The purpose is to enable bonding with a small heat capacity and prevent positional displacement and thermal deterioration of electronic components.

[Means for Solving the Problems] The electronic component of the present invention is an electronic component that includes a lead for connection to another electronic circuit element, and includes a lead surface other than the bonding area where the other electronic circuit element is bonded. It is characterized in that the entire area or at least a portion of the area is covered with a material having high thermal emissivity.

Moreover, a metal oxide can be used as the material having a high thermal emissivity.

[Function] In the present invention, since the entire area or at least a part of the area other than the bonding area on the lead surface is covered with a material with high thermal emissivity, the bonding area of the lead is covered with other electronic circuits such as wiring pads. When light (infrared) energy such as a laser beam is irradiated onto an area covered with a material with high thermal emissivity, the light energy is efficiently absorbed and the leads and other electronic circuit elements are exposed in a short period of time. It can be joined as follows. Furthermore, since the leads are covered with a material with high thermal emissivity, heat dissipation is good immediately after bonding, and the cooling rate of the leads is fast.

Therefore, the thermal energy supplied to the lead joint can be reduced, and the heat dissipation immediately after the lead is joined is also good.
The temperature of the electronic component does not rise when the leads are joined, and thermal deterioration of the electronic component can be prevented. Furthermore, by reducing the thermal energy required for lead bonding, a low-power heat source such as a laser beam irradiation device can be used, resulting in energy savings.

Furthermore, since the lead surface is covered with a material with high thermal emissivity and the lead is cooled quickly immediately after bonding, the lead is less likely to be misaligned. Furthermore, since misalignment of the leads can be prevented, even if the pitch between the leads is narrowed, short circuits between the leads are less likely to occur, making it possible to narrow the pitch of the leads.

In addition, if metal oxides are used as materials with high thermal emissivity,
Since it also has electrical insulating properties, it reduces the possibility that the leads will show up due to solder bridges, etc. in the process of mounting electronic components on wiring boards and the like. Furthermore, a region with high thermal emissivity can be formed at low cost by simply oxidizing a portion of the surface of the metal lead.

"Example code" DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail based on the accompanying drawings.

FIG. 1 shows an electronic component according to an embodiment of the present invention.

In this electronic component, one end of a metal lead 4 is bonded to the bump 3 on the electrode pad 2 of the paired chip ICI. This lead 4 has a metal core plated with tin, silver, gold, etc. on the surface, and the joint surface 4 of the lead is plated with tin, silver, gold, etc.
A high thermal emissivity layer 5 made of a material with high thermal emissivity ε, such as a metal oxide, is formed on the entire surface (upper surface) opposite to a.

When mounting this paired chip ICI on the wiring pad 7 of the wiring board 6, pre-solder 8 is applied on the wiring pad 7 in advance, and the paired chip ICI with the leads 4 fixed to a film or tape is mounted on the wiring board 6. The bonding surface 4 of the lead 4 is placed on the wiring pad 7 from above the preliminary solder 8.
1 and 2, the surface of the high thermal emissivity layer 5 is irradiated and scanned with laser light α to melt the solder 8, and connect the leads 4 to the wiring pads 7.
solder to. Then, when the laser beam α is irradiated onto the joint (the irradiation spot of the laser beam α is shown in FIG. 2), the laser beam (infrared rays) α is efficiently absorbed from the high thermal emissivity layer 5, leading to Heat is transmitted from the bonding surface 4a of 4 to the preliminary solder 8 to melt the preliminary solder 8 in a short time. - When the irradiation of the radiation α is stopped, the heat of the lead 4 is quickly radiated into the air through the waste heat emissivity layer 5, and the lead 4 is cooled. Therefore, the pair of chips CI is cooled down before it reaches a high temperature, and its thermal deterioration is prevented. Furthermore, since the high thermal emissivity layer 5 provides good heat absorption, a laser beam irradiation device with a small output can be used. Furthermore, since the thermal cooling after melting the solder becomes rapid, the leads 4 are less likely to be displaced from the wiring pads 7. moreover,
The heat generated by the paired chip ICI can be dissipated from the leads 4 not only during the bonding process of the base 7-chip ICI, but also when the paired chip ICI is driven due to the high radiation from the lead 4, extending the life of the paired chip ICI. can be kept.

As the high thermal emissivity layer 5, for example, metal oxide can be used as described above. Figure 3 shows various metals (AQ
, Ni, Si, Nb, etc.). As is clear from this figure, the thermal emissivity ε of the metal molten metal is high. For example, if ε>0°8, the heating efficiency will be ten times greater than that of the plated surface of the lead 4. Moreover, since tin, silver, gold, or the like is generally used for plating the leads 4, the high thermal emissivity layer 5 of metal oxide can be easily formed by oxidizing these plating metals. . For example, tin and silver can be easily oxidized, and the plating surface of the lead 4 may be oxidized electrochemically or chemically before the lead 4 is attached to the paired chip CI. Also, the depth of oxidation is 0.5Ln
It is enough. In this way, forming a metal oxide layer on the surface of the lead 4 increases the thermal emissivity of the surface of the lead 4, making it easier to absorb heat (infrared rays) and cooling. Electrical insulation reduces electrical short-circuit accidents caused by solder bridges or lead contact.

The high heat reflectance layer 5 is not limited to metal oxides, and may also be made of graphite powder (ε=0.97) or glass (
ε=0.9), enamel (ε and 0°9~0.95), *
Ceramics with large ε such as (ε#0.90-0.97), rubber (ε=0.8-0.95) and cellulose resin (ε'-=0.7-0.9) , black paint (ε-
A chemical synthetic product with a large ε such as 0.95) may also be used, and these may be applied to the surface of the lead 4.

According to the present invention, since soldering can be done by solidifying the solder in a short time afterwards, misalignment of the leads is less likely to occur. For this reason, we reduced the width of the lead and made it thinner.
It becomes possible to provide a large number of leads at a narrow pitch.

For example, what is shown in FIG. 4 is an electronic component in which leads 4 having a width W of 30 to 40 tn are provided at a pitch of p-70 stiffness. When the leads 4 are made thinner in this way, it becomes difficult for heat to travel through the leads 4 and escape to the paired chip ICI side, so the effect of providing the high thermal emissivity layer 5 is noticeable at the joint and prevents solder leakage on the joint surface 4a. Improves sex. For this reason, Figure 5 (
When the lead 4 formed into the shape shown in a) is heated and the solder 8 melts, the entire joint surface 4a of the lead 4 leaks into the solder 8, and then the solder 8 melts as shown in FIG. 5(b). : 4 sticks to the wiring batt 7 due to the leakage of the solder 8, and when the irradiation of the laser beam α is stopped, as shown in Fig. 5 (b
), the solder 8 quickly solidifies with the lead 4 stuck to the wiring bat 7. Therefore, even if the REIT 4 is misaligned and the narrow pitch portion 4 is formed, it can be bonded to the wiring pad 7 without shorting. Further, if the leads 4 are covered with the high thermal emissivity layer 5, heat radiation can be improved even when the leads 4 are arranged at high density.

Furthermore, even in the case of a large lead width, the lead 4 can be made with holes 9 as shown in FIG. 6, or constrictions 10 on both sides of the lead 4 as shown in FIG.
Even if the cross-sectional area is partially reduced, the transfer of heat from the junction to the paired chip ICI side can be reduced.

The high thermal emissivity layer 5 may be applied to both the front and back surfaces of the leads 4, leaving only the bonding surfaces 4a. Alternatively, as shown in FIG. 6, the high thermal emissivity layer 5 may be provided only at the laser beam irradiation locations including the joints.

What is shown in FIG. 8 is still another embodiment of the present invention, in which a wiring pad 7 having a bump 13 is provided at the tip of a circuit pattern 11, and a laser beam on the wiring board 6 except for the wiring butt 7 and its vicinity is provided. Coat 1 with high thermal emissivity covers the light irradiation area
It is covered by 2. For this reason, as shown in Fig. 8, the lead 4
When the laser beam α is irradiated to the bonded portion of the Anda, heat is applied to the Anda from the wiring board 6 side, and after bonding, heat can be quickly dissipated from the wiring board 6 side as well.

In the above embodiments, the case where the leads are soldered is described, but the present invention may also be used when the leads are joined between metals to a wiring bat, etc., and is not limited to the case where the leads are heated with laser light. It is also effective in the case of tool heating such as thermocompression bonding.

[Effects of the Invention] In short, according to the present invention, the temperature of the electronic component does not increase during lead bonding, and thermal deterioration of the electronic component can be prevented. Furthermore, the heat source such as the laser beam irradiation device can be of low power, resulting in energy savings. Furthermore, since the leads are cooled quickly immediately after bonding, the leads are less likely to be misaligned. Furthermore, since misalignment of the leads can be prevented, even if the pitch between the leads is narrowed, short circuits between the leads are less likely to occur, making it possible to narrow the pitch of the leads.

In addition, if a high thermal emissivity layer made of metal oxide is formed,
Since it has electrical insulating properties, it reduces the risk of short-circuiting of leads due to solder bridges, etc. in the process of mounting electronic components on wiring boards and the like. Further, high thermal emissivity can be reduced at low cost by simply oxidizing a part of the surface of the metal lead.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway front view showing one embodiment of the present invention;
Figure 2 is a plan view showing one of the leads of the electronic component and its surroundings, Figure 3 is a diagram showing the thermal emissivity of several types of metal oxides, and Figure 4 is another example of the present invention. FIGS. 5(a) and 5(b) are partially enlarged views showing how the same leads are soldered, and FIG. 6 is a partially broken perspective view showing an embodiment of the present invention. FIG. 7 is a perspective view showing a part of the lead in still another embodiment of the present invention, and FIG. 8 is a partially broken perspective view showing still another embodiment of the present invention. 9 is a partially broken perspective view of a conventional example, FIG. 10 is a partially broken perspective view showing another conventional example, and FIG. 11 is a diagram showing the thermal emissivity of several types of metals. . l...Pair chip IC 4...Lead 4a...Lead bonding surface 5...High thermal emissivity layer 7...Wiring pad

Claims (2)

[Claims] (1) An electronic component equipped with a lead for connection to another electronic circuit element, in which the entire or at least a portion of the area other than the bonding area where the lead surface is bonded to the other electronic circuit element has a thermal emissivity. An electronic component characterized by being covered with a high quality material. (2) The electronic component according to claim 1, wherein the material with high thermal emissivity is a metal oxide.