JP2014099574A - Lead frame heat releasing substrate and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low cost heat conduction substrate excellent at large current, high heat releasing, and high temperature, to provide a manufacturing method suitable also for production having a background of mass- production with multiple faces in a short step, and to provide a lead frame substrate capable of providing a large current circuit and a fine conductor circuit at the same time.SOLUTION: A heat conduction substrate includes, for a large current and excellent heat releasing usage, a high heat conduction material (including a filler) for an intermediate layer of a metal plate 6 and a lead frame. Or, the heat conduction substrate is a substrate of a laminate structure formed by thermal curing of a low elasticity resin. Spaces between adjacent surface layer conductor circuits are protected by a flattening resin. A large current thick copper circuit and a fine conductor circuit 8 may be integrated (provided side by side) at a same height as the lead frame.

Description

The present invention relates to a current control circuit using a conventional power semiconductor, a next-generation power semiconductor, a power module, and the like of an electronic device, an optimum heat conductive substrate capable of withstanding a large current and a high temperature, and a method for manufacturing the same.

In recent years, with the demand for higher performance and smaller size of electronic equipment, circuit modules using conventional and next-generation power semiconductor (SiC) power electronic components have high current, high heat dissipation and further miniaturization. It has been demanded. In addition, since power electronic components (for example, power semiconductor elements) are accompanied by large current and high heat generation, it is necessary to mount them on a heat conductive substrate corresponding to large current and high heat dissipation. Substrates that take heat dissipation and mountability into account have become necessary.

With the improvement in performance of industrial equipment such as control equipment and motors, the transition of high power and high current modules such as high power and high efficiency inverters has progressed, and large amounts of heat have been generated and increased from power semiconductor elements and large currents. . Electric vehicles (EV), hybrid vehicles (HEV), robots, solar power generation, wind power generation power conditioners, industrial motors, etc., use SiC (silicon carbide) for large current control, high power power supplies, motor circuits, etc. In order to efficiently dissipate this heat as the electrical load is reduced with a large electrical load in the application, at present, the high power module substrate has a ceramic substrate such as aluminum nitride or silicon nitride that has thermal conductivity in accordance with the requirements, and its In many cases, a metal plate such as a copper plate or an aluminum plate is bonded to the front and back.

On the other hand, as a technology to improve heat dissipation from the cost aspect, an aluminum metal substrate or a copper metal substrate is used for a conventional printed circuit board made of glass epoxy resin, and a conductor circuit is formed through an insulating layer on one side or both sides. Metal base substrates to be formed are known. Aluminum metal substrates are suitable for low-power applications, but there are problems such as insufficient heat dissipation.

In addition, ceramic substrates such as alumina and aluminum nitride are often used for substrates that require high current, high heat dissipation, and thermal conductivity. It has excellent heat resistance and heat dissipation and can withstand 300 to 400 ° C. However, ceramic substrates and the like are still expensive and have problems such as mechanical impact, weakness in strength, and brittleness.

Japanese Patent No. 3214696

Since the above metal base substrate and ceramic substrate are difficult to achieve in terms of specifications, performance and cost, a heat conduction module by injection molding in which a lead frame is integrated with a thermoplastic resin has been proposed. However, there is a limit because the molding surface cannot be sufficiently filled with a filler and there are problems such as poor heat dissipation. Therefore, the metal base substrate and the ceramic substrate have been a major issue in terms of both performance and cost.
In addition, it is difficult to arrange a thick conductor circuit pattern for a large current and a fine conductor circuit on the same surface.

Based on such a background, the lead frame substrate of the present invention is a heat dissipation substrate that is excellent in large current characteristics, heat dissipation characteristics, cost, etc., and can be mounted with a heat generating component. By combining high heat conductive fillers and selecting various resins such as heat conductivity of 2 W / mK or higher and heat resistance of 250 ° C. or higher as an example, heat dissipation efficiency can be increased and low cost manufacturing can be achieved with fewer manufacturing processes. A manufacturing method is provided.
In addition, since a fine conductor (thin copper) circuit and a large current (thick copper) circuit can be provided on the same surface, it is possible to provide a substrate for a power device that is smaller in size and has high heat dissipation efficiency.

The present invention has a structure in which a high thermal conductive material (insulating resin) is laminated on an intermediate layer between a metal plate and a lead frame, and an insulating layer is applied and protected between the adjacent lead layer lead frames with a smoothing agent (flattening resin). This is a heat conductive substrate that can provide high current and high heat dissipation with the lead frame circuit surface and the protective insulating layer flush with each other.
As the smoothing agent, those composed mainly of an epoxy resin, a phenol resin or the like can be used.
As the lead frame material, oxygen-free copper (symbol: C1020), tough pitch copper (symbol: C1100), and other copper alloys, mainly copper, can be used.
On the other hand, it is also possible to apply a fine conductor circuit between the conductors of the lead frame. In that case, after applying electroless copper plating and electrolytic copper plating to the surface layer part including the conductor and the protective insulating layer, the photosensitive property Necessary conductor circuits are formed by liquid etching resist (or photosensitive dry film etching resist), exposure, development, and etching.

The present invention is characterized in that it is possible to realize a low-cost substrate with high reliability and high heat dissipation for high-current applications by reducing the above-mentioned problems with a few manufacturing processes.

As the insulating layer used for the intermediate layer of the present invention, commercially available high thermal conductive resins, low elastic resins, and the like can be used. A thermosetting resin having a thermal conductivity of 5 W / mK or higher and a heat resistance of 250 ° C. or higher has already been developed.
The insulating layer is preferably made of a woven or non-woven fiber such as a heat-resistant glass cloth because it is easy to ensure mechanical strength, withstand voltage and heat resistance. In addition to high heat dissipation, a substrate can also be formed using a low-elasticity resin with high reliability that can withstand severe temperature cycle environments and solder cracks.

When creating a fine conductor circuit between the conductor circuits of the lead frame, as an example, electroless copper plating and electrolytic copper plating are applied to the circuit surface side to about 25 to 50 μ, and then a photosensitive etching resist, exposure, A fine conductor circuit can be formed by performing development and a copper etching process.

A schematic manufacturing process based on the embodiment of the lead frame heat dissipation board of the present invention is as follows.
The embodiment is a type in which the lead frame conductor pattern is first formed by die outer shape press or etching and then laminated, and since the conductor cross section of the lead frame can be formed in a vertical shape, the accuracy between adjacent conductor circuits is improved. It is suitable for increasing and mass productivity. Example 1
Another embodiment is a type in which a lead frame before conductor pattern formation is laminated and adhered, and then the lead frame surface is etched to form a conductor circuit. (Example 2)
In this case, in order to ensure electrical insulation from the adjacent conductor circuit, it is necessary to secure an appropriate space at both the top and bottom of the conductor pattern. Since it is affected by the etching factor, it can be applied when the gap accuracy between the conductor circuits can be relaxed, or when the line / space (100 μm to 1 mm) of the fine conductor circuit is unnecessary or large.

(Process overview of Example 1)
(A) Lead frame pattern creation Mold press or etching process into a predetermined conductor pattern shape (b) Copper or aluminum base plate, insulating layer (thermally conductive, low elastic resin), lead frame Laminated up by three layers (c) Lamination process by hot pressing (d) Buff polishing of surface layer part, Chemical polishing process (e) Roughening process of surface layer part (f) Smoothing agent (under) (Coating) Application process (g) Mechanical polishing (ceramic buffing) process (h) In the case of forming a fine conductor circuit between the lead frames, after the desmear is performed as necessary, the entire copper plating process is performed (i) Photosensitive etching Resist (laminate), pattern exposure, development, copper etching, forming resist circuit through resist stripping process (j) solder resist coating process (k) surface treatment after circuit formation ( i plating, Au plating, etc.) processes, and trimmed

(Process overview of Example 2)
(A) Copper or aluminum base plate, insulating layer (thermal conductivity, low-elasticity resin), lead frame with a structure in which three layers are stacked in order, (b) Lamination process by hot pressing (c) Surface metal part A conductive circuit of a surface layer lead frame is formed by photosensitive etching resist (laminate), exposure, development, and copper etching. (D) Surface buff polishing, chemical polishing step (e) Surface layer roughening step (f) Lead frame Smoothing (undercoat) coating process on the surface (g) Surface layer mechanical polishing (ceramic buffing) process (h) In the case of forming a fine conductor circuit between the lead frames, the entire copper plating process is performed (i) Photosensitive etching resist (Lamination), pattern exposure, development, copper etching, resist stripping process to form a conductor circuit (j) If the conductor circuit surface has large irregularities, Over the resist coating step (k) the surface treatment after the circuit formation (Ni plating, Au plating, etc.) processes, and trimmed

According to the present invention, it is possible to provide a low-cost lead frame heat dissipation board excellent in high current and high heat dissipation. In addition, a conductor circuit of a large current (thick copper) circuit and a control (thin copper) circuit can be provided.
Since the substrate can be manufactured in a short process, it is suitable for production against the background of mass productivity. Unlike a small-sized substrate such as a ceramic substrate, productivity can be increased because a substrate manufacturing process with multiple surfaces can be easily performed.
By selecting an insulating layer for next-generation power semiconductors and the like, it is possible to provide an optimum thermal conductive substrate that can withstand high currents and high temperatures that are suitable for impact resistance, severe temperature cycling, heat dissipation, and the like.

Outline lamination layup explanatory diagram showing the form of the embodiment Schematic cross-sectional explanatory diagram showing the form after lamination Schematic cross-sectional explanatory diagram showing the form after applying the flattening resin Schematic cross-sectional explanatory drawing showing the state of substrate surface flattening Schematic cross section of lead frame and fine conductor circuit Schematic plan view of lead frame and conductor circuit Schematic plan view of lead frame and conductor circuit (after outline processing) Schematic plan view of lead frame and conductor circuit (after etching process)

1: Hot plate 2: Cushion material (release paper)
3: Press plate (SUS)
4: Lead frame material 5: Insulating material (thermal conductive material, low elastic resin, etc.)
6: Metal plate (copper, aluminum material, etc.)
7: Smoothing agent (flattening resin)
8: Fine conductor circuit

FIG. 1 in Example 1 shows an example of layup when laminating by hot pressing.
A heat conductive insulating material 5 and a lead frame material 4 are stacked on a metal plate 6 serving as a base of a lead frame substrate, and a cushioning material 2 having releasability is placed on both sides of the metal plate 6 and sandwiched between press plates 3. preferable. A release paper such as a cushioning material 2 is placed between the hot plate 1 of the hot press and the press plate 3 using SUS, etc., so as to prevent dents and make the pressing force uniform.
As the lead frame material, various alloys, oxygen-free copper (symbol: C1020), tough pitch copper (symbol: C1100), and the like can be selected. For example, the thickness is about 0.2 mm to 1 mm. The material and thickness can be selected and optimized according to processability, electrical conductivity, and current capacity. Etching may be used as a method for forming a lead frame conductor pattern, but punching with a die press is suitable in terms of pattern identity and mass productivity.
In the case of a die press, burrs and the like are likely to occur. Therefore, a polishing process is performed before laying up to remove and smooth the burrs.

As the metal plate 6 serving as a base, a copper plate, an aluminum plate, an alloy, or the like is usually used. In the case of a copper plate, oxygen-free copper (symbol: C1020), tough pitch copper (symbol: C1100), etc. are often used. As the insulating material 5, a sheet-like base material (prepreg) made of a reactive curable resin such as glass fiber, polyimide resin, and epoxy resin can be used. Various products are commercially available, and any of them can be selected and used according to their specifications. In order to keep the flatness, thickness and strength of the insulating layer constant, glass fiber is preferable.
In particular, an insulating material using a low-elasticity resin is suitable for an environment where temperature cycle conditions are severe, in order to prevent a solder crack caused by thermal expansion with a mounted component.

The thinner the heat conductive insulating layer, the higher the heat dissipation characteristics. On the other hand, the withstand voltage tends to decrease, so the insulation thickness that satisfies the withstand voltage specification is selected and optimized. The thickness of the insulating layer is often set to a thickness of 50 μ to 0.2 mm in consideration of withstand voltage and thermal conductivity, for example.
As an example, a product having an insulation layer with a glass fiber-containing thickness of 100 μm (3 W / mK) and a withstand voltage of 4 kV has already been provided. In addition, thermosetting resins having a thermal conductivity of 5 W / mK or higher and a heat resistance of 250 ° C. or higher have already been developed.

After the layup, lamination by hot pressing is performed according to the temperature profile selected by the resin, and as a result, a laminate shown in FIG. 2 can be obtained.
As an example, the curing temperature for the resin by hot pressing is in the range of 160 ° C. to 180 ° C., and the pressure is suitably 2 to 3 MPa.
In the hot press, the lead frame material 4 is superposed on the insulating resin 5, and a copper plate 6 or the like is sandwiched between the bases, and heating and pressurizing processes are performed to bond them by thermosetting. In order to increase the adhesion with the resin, it is preferable to mechanically and chemically roughen the surface where the lead frame surface and the insulating layer of the base surface are bonded in advance in order to increase the adhesion.

FIG. 2 of Example 1 is a cross-sectional view showing a form after lamination, and shows a cross-sectional state after lamination of the lead frame material 4, the insulating material 5, and the metal plate 6 based on the layup of FIG. The lead frame material 4 and the insulating material 5 are in intimate contact, but the surface portion is uneven and does not become smooth. A part where the lead frame material 4 is formed is a convex shape, and a part where the lead frame material 4 is not is a concave shape.

FIG. 3 of Example 1 is a cross-sectional view showing the form after the application of the planarizing resin, and in order to smooth the surface, the smoothing agent 7 is applied to the concavo-convex portion on the lead frame material 4 side with a screen mesh, After pre-curing at 120 ° C., heat curing at 180 ° C. The smoothing agent 7 is, for example, a thermosetting undercoat, and is excellent in chemical resistance, heat resistance and mechanical strength, which is mainly composed of an epoxy resin and contains phenol, and is flat on a substrate having a copper thickness of 400 μm or more. It can be applied to This resin is also suitable for thin small substrates because of its excellent bending resistance.
In the case where particularly high heat resistance is required as the planarizing resin, a silicon-containing resist such as a silicon resin can be selected.

FIG. 4 of Example 1 is a schematic cross-sectional view showing a state of flattening the substrate surface. As an example, a ceramic buff or the like is used for the substrate after application of FIG. 3 (conveyor speed: about 1 m / min). Polish the surface including the frame material. By polishing until the lead frame surface is exposed to the surface, the surface is flattened. As a result, the entire surface of the lead frame between the conductor surface and the adjacent surface can be made flush.

FIG. 5 is a cross-sectional view showing a state when the fine conductor circuit 8 is added to the lead frame surface.
For example, the surface of the flattened substrate shown in FIG. 4 is uniformly plated to a thickness of 20 to 50 μm by combining a plating catalyst such as palladium with a combination of electroless plating and electrolytic plating.
For the electroless plating, a plating solution such as copper or nickel is used. However, since the conductor circuit 8 is formed by copper etching after that, copper is preferable.
After the entire surface is subjected to electrolytic copper plating, a photosensitive etching resist or the like is laminated, and exposure, development, and etching are performed according to the pattern shape of the conductor circuit 8 to form.
After the etching, the remaining dry film etching resist or the like is peeled off with an aqueous sodium hydroxide solution, and then washed and dried, whereby the fine conductor circuit 8 can be formed.

FIG. 6 is a plan view of the substrate with the lead frame frame and the conductor circuit attached together according to the embodiment as seen from above.
Since the conductor circuit portion and the lead frame frame are connected and laminated together, each conductor can be brought into close contact with the insulating resin at a predetermined position.
The shaded portion visible from the upper surface is a conductor circuit and a wiring circuit of the lead frame, and the other portions are protected by being filled with an insulating resin or a solder resist with a smoothing agent 7.
Since all the conductors of the lead frame are connected, when electrolytic plating or the like is required for the surface treatment, it can be used as a plating lead, and a new plating lead is not necessary and can be easily implemented.
The outer peripheral portion of the lead frame frame is processed in a subsequent process. FIG. 7 shows the outer shape after processing. As an example, the outer shape is finished so that burrs are not generated on the mounting surface side by punching from the back surface with a die press.
A cut surface of AA ′ is shown in FIG. 5, and a structure in which a metal plate on the bottom is laminated with a resin having high electrical insulation, which is a combination of a thermosetting resin and a high thermal conductive material, and a conductor circuit on the top is understood from the drawing. .

The lead frame substrate of FIG. 8 in the embodiment is suitable for specifications and applications in which a conductor pattern and leads are not provided around the end face of the substrate in order to further increase the withstand voltage.
As a manufacturing method in this case, the lead frame is implemented in the following steps without forming a conductor pattern in advance.
An insulating material 5 having thermal conductivity and a lead frame material 4 not formed with a conductor are superimposed on a metal plate 6 serving as a base of the lead frame substrate, and a cushioning material 2 having releasability is placed on both sides thereof, and a press plate 3 is preferable. A release paper such as a cushioning material 2 is placed between the hot plate 1 of the hot press and the press plate 3 using SUS, etc., so as to prevent dents and make the pressing force uniform. As the lead frame material on which no conductor is formed, various alloys, oxygen-free copper, tough pitch copper, and the like can be selected. The thickness is, for example, about 0.2 mm to 1 mm, and is selected according to the module specifications. The material thickness is selected and optimized depending on the current capacity and the like.

In the hot press, the lead frame material 4 is overlaid on the insulating resin 5, and the base plate is sandwiched between the copper plate 6 and the like, and is heated and pressurized to be bonded by thermosetting. In order to increase the adhesion with the resin, it is preferable that the adhesive surface between the lead frame surface and the insulating layer of the base surface is roughened mechanically and chemically in advance in order to ensure adhesion.
After laminating by hot press, in order to form a conductor circuit on the lead frame, laminating a photosensitive etching resist, etc., carrying out the steps of exposure, development, copper etching, resist stripping, and forming a conductor pattern on the surface layer part . In the case of thick copper, in consideration of the influence of the etch factor, it is necessary to secure a wide space between the conductors in proportion to the thickness of the circuit.

The lead frame material 4 and the insulating material 5 are in close contact with each other, but the surface portion is uneven and uneven, and the lead frame material 4 has a convex shape in the conductor portion and a concave shape in the portion without the conductor. In the process subsequent to FIG. 3 in the above-described embodiment, a flattening resin coating, a surface polishing process, a final conductor circuit formation, etc. are performed, and surface plating is performed to manufacture a lead frame substrate.

A schematic manufacturing method of the lead frame substrate of Example 1 is shown below.
1) A lead frame material 4 after etching or press-cutting is formed on a rolled copper plate (or AL plate) serving as a base by hot pressing. The copper plate and the lead frame material 4 (usually about 1 mm in many cases) are roughened in advance to measure the adhesion strength with the insulating layer.
As the insulating resin (prepreg), an appropriate resin is selected from high heat resistance, high thermal conductivity, low elasticity, and the like according to applications.
2) After the substrate lamination is completed by hot pressing, the substrate is taken out and the surface of the metal part is smoothed by mechanical polishing, chemical polishing or the like. Next, in order to apply the smoothing agent 7, the surface is roughened in advance.
After that, since the surface has a structure in which the lead frame material 4 is laminated, the surface of the lead frame material 4 and the insulating layer has uneven steps.
A smoothing agent (flattening resin) or the like is printed and applied over the entire circuit surface in order to fill the unevenness of the lead frame and the insulating layer 5.
After applying the smoothing agent 7, the resin (insulating layer) between the lead frames is cured.
After the resin (insulating layer) is cured, the surface of the smoothing agent 7 and the lead frame circuit surface are flattened with a ceramic buff.
3) When a fine conductor circuit is formed between adjacent lead frames, electroless copper and electrolytic copper plating are performed on the entire surface. As an example, a plating thickness of usually 20 μ to 50 μ is preferable.
A conductive circuit is formed through a photosensitive etching resist (laminate), pattern exposure, development, copper etching, and resist stripping process. A solder resist is applied to the conductor circuit surface.
4) Depending on the specifications, surface treatment (N plating, gold plating) after forming the conductor circuit is performed.

A schematic manufacturing method of the lead frame substrate of Example 2 is shown below.
1) The copper plate and the lead frame material 4 (usually about 1 mm) are roughened in advance to measure the adhesion strength with the insulating layer.
As the insulating resin (prepreg), an appropriate resin is selected from high heat resistance, high thermal conductivity, low elasticity, and the like according to applications.
2) After substrate lamination is completed by hot pressing, the substrate is taken out and the surface is smoothed by buffing, chemical polishing or the like. The conductor circuit of the lead frame material is formed through a photosensitive etching resist, exposure, development, copper etching, and peeling process.
Next, in order to apply the smoothing agent 7, the surface is roughened.
Since the surface has a structure in which the lead frame material 4 is laminated, the surface of the lead frame material 4 and the insulating layer has uneven steps.
A smoothing agent (flattening resin) or the like is printed on the front surface to fill the unevenness of the lead frame and the insulating layer 5.
After applying the smoothing agent 7, the insulating layer between the lead frames is cured.
After the insulating layer is cured, the smoothing agent 7 surface and the lead frame circuit surface are flattened with a ceramic buff.
If there is no fine conductor circuit between adjacent lead frames, solder resist is applied as it is.
3) When a fine conductor circuit is formed between adjacent lead frames, panel plating of electroless copper and electrolytic copper plating is performed on the entire surface. As an embodiment, a plating thickness of 20 μm to 50 μm is usually preferable, but it is possible to correspond to an appropriate plating thickness according to the specification.
A conductive circuit is formed through a photosensitive etching resist (laminate), pattern exposure, development, copper etching, and resist stripping process. Apply solder resist to the conductor circuit surface.
4) If necessary, surface treatment (N plating, gold plating) after forming the conductor circuit is performed.

Due to the manufacture of the lead frame substrate according to the above embodiment, the structure is designed to withstand the large current (thick copper) circuit with increased conductor thickness including the control (thin copper fine conductor) circuit and the heat generated by the circuit. By mounting device parts, package parts, etc., it is possible to provide a heat conduction substrate that improves heat dissipation and diffusibility and solves problems suitable for extending the life of parts.

Claims (4)

It is a heat conductive substrate consisting of a metal plate, a heat conductive insulating layer or a low elastic insulating layer and a lead frame. The space between the lead frames is protected by a smoothing agent (flattening resin), and the large current conductor circuit and the fine conductor circuit are coplanar. Lead frame substrate for high heat dissipation that can be integrated (co-located). The lead frame is a lead frame substrate according to any one of copper plates including tough pitch copper, oxygen-free copper, and other alloys The above-mentioned heat conductive insulating layer is a lead frame substrate including a thermosetting resin and a high heat conductive filler (including epoxy) or a low elastic resin. 2. A method of manufacturing a lead frame substrate according to claim 1.

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