Lead frame and surface treatment method thereof

Abstract

The invention provides a lead frame and a surface treatment method thereof, and the method comprises the steps: carrying out an ultrasonic sand blasting process after a metal thin material electroplating process, and the ultrasonic sand blasting process comprises carrying out sand blasting treatment on an electroplated metal thin material under an ultrasonic condition until the surface of the metal thin material meets a preset roughness requirement. According to the method, the surface of the plating layer is polished through ultrasonic sand blasting, stripes formed by material calendering lines or protrusions and sand holes caused by particles on the surface of the plating layer are polished to be flat, the surface quality consistency of the lead frame is improved, the situation that a photosensitive film falls off in the later procedure is effectively improved, and therefore the use performance and the yield of a lead frame product are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lead frame manufacturing, and in particular to a lead frame and a surface treatment method thereof. Background Art

[0002] Lead frames are the conductive carriers of integrated circuits and chip packages. They are the key structural parts for realizing the electrical connection between the internal circuit leads of the chip and the external leads to form an electrical circuit. They also provide mechanical support for the chip and, together with the package shell, dissipate the heat generated by the chip when it is working. Lead frames are required in most semiconductor integrated blocks and are an important basic material in the electronic information industry. Their quality is directly related to the reliability and service life of the integrated circuit.

[0003] Lead frames are usually made of metal sheets by calendering, and their surfaces generally need to be processed through multiple processes such as unloading-development-electroplating-washing-film stripping-washing-drying-receiving-film coating to improve their corrosion resistance, electrical properties, wear resistance, and packaging properties. During electroplating, the metal sheets will be affected by the calendering lines of the calendered materials, forming irregular stripes on the surface of the coating. There will also be protrusions or sand holes caused by particles, making the surface of the coating uneven, thus affecting the adhesion between the thin material coating and the photosensitive film during the secondary lamination.

[0004] The invention patent with publication number CN115472507A discloses a high-reliability lead frame sandblasting process and its products, which uses a sandblasting agent to wet-blast the lead frame after secondary die-cutting, film stripping and silver plating, so that the surface of the lead frame has a certain degree of roughness and cleanliness. However, due to the agglomeration of tiny sand particles in the liquid and the uneven sandblasting liquid during wet sandblasting, the stability and consistency of the lead frame surface quality are affected.

[0005] The invention patent with publication number CN112563144A discloses a lead frame surface treatment process, which uses physical sandblasting roughening after chemical roughening to improve the roughening effect of the lead frame while improving the roughening consistency, and adds ultrasonic impurity removal and anti-oxidation processes to improve the quality of lead frame surface treatment. After sandblasting, the patent performs ultrasonic treatment to remove impurities remaining on the surface, but during the sandblasting process, the sand particles still agglomerate, resulting in the local roughness being significantly greater than other locations when the sandblasting surface is roughened, and the surface roughness inconsistency has not been significantly improved.

[0006] Therefore, there is an urgent need for a surface treatment method for a lead frame, which can effectively solve any of the following problems: surface defects and unevenness of the lead frame coating caused by the calendering texture of the metal foil, insufficient adhesion between the coating and the photosensitive film, easy detachment of the photosensitive film, uneven agglomeration of the sandblasting agent, and inconsistent roughness of the lead frame after sandblasting. Summary of the invention

[0007] In view of the defects in the prior art, an object of the present invention is to provide a lead frame and a surface treatment method thereof.

[0008] The present invention is achieved through the following technical solutions:

[0009] According to one aspect of the present invention, a surface treatment method for a lead frame is provided, the method comprising: performing an ultrasonic sandblasting process after a metal thin material electroplating process, the ultrasonic sandblasting process comprising sandblasting the electroplated metal thin material under ultrasonic conditions until the surface of the metal thin material reaches a preset roughness requirement.

[0010] Optionally, in the electroplating process, the electroplating time is 5 to 50 seconds, the electroplating temperature is 30 to 80° C., and the coating thickness is less than 1 μm.

[0011] Optionally, in the ultrasonic sandblasting process, the sandblasting particle size is 200-500 mesh, the sandblasting time is 10-100 seconds, the sandblasting depth is 0.05-0.2 μm, and the ultrasonic frequency is 10-100 kHz.

[0012] Optionally, before the electroplating process, a material discharging process and a developing process are also included, and the developing process is after the material discharging process.

[0013] Optionally, the unloading process includes placing the metal thin material coil processed by the previous exposure process into the unloading station, wherein: the thickness of the metal thin material is 0.01-0.2 mm;

[0014] The developing process includes developing the plate-making pattern on the metal thin material with a developer, wherein the developer is any one or more of Na2CO3·10H2O, K2CO3 and copper sulfate, and the developing time is 30 to 300 seconds.

[0015] Optionally, after the ultrasonic sandblasting process, a first water washing process, a film stripping process, a second water washing process, a drying process, a material collecting process and a film coating process are sequentially included.

[0016] Optionally, in the film stripping process, the film stripping liquid is potassium hydroxide, the film stripping temperature is 30 to 100° C., and the film stripping time is 100 to 600 seconds.

[0017] Optionally, in the drying process, the drying temperature is 30 to 120° C., and the drying time is 0.5 to 100 minutes.

[0018] Optionally, the laminating process includes: adhering a photosensitive film to the surface of the metal thin material by a laminator, and then placing and fixing a product pattern to be produced on the outer surface of the photosensitive film to obtain a lead frame product with a photosensitive film;

[0019] Wherein: the material of the photosensitive film is any one or more of polyimide, photoresist, polyethylene and polyester film, and the thickness of the photosensitive film is 0.01-0.1 mm.

[0020] According to another aspect of the present invention, a lead frame is provided, which is manufactured using the above-mentioned surface treatment method of the lead frame.

[0021] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0022] The surface treatment method of the lead frame provided by the present invention is to polish the surface of the coating by ultrasonic sandblasting after the metal thin material is electroplated, so that the stripes formed on the coating surface due to the material rolling lines or the protrusions and sand holes caused by the particles are polished flat, so that the surface of the electroplated layer is flat and the coating has a good surface state. Since the sandblasting is performed under an ultrasonic environment, the agglomeration of sand particles can be reduced, so that the dispersion of the sand particles is greatly improved, and the problem of the metal foil material in the existing process having a sudden change in the surface roughness of the local area after sandblasting is solved, and the surface quality consistency of the lead frame can be improved, and the situation of the photosensitive film falling off from the lead frame in the subsequent process can be effectively improved, thereby improving the quality stability, performance and yield rate of the lead frame product. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0024] Figure 1 The figure is a schematic flow chart of a surface treatment method of a lead frame according to an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0026] Reference Figure 1As shown, an embodiment of the present invention provides a surface treatment method for a lead frame. The method includes: performing an ultrasonic sandblasting process after the metal thin material electroplating process, and the ultrasonic sandblasting process includes sandblasting the electroplated metal thin material under ultrasonic conditions until the surface of the metal thin material reaches the preset roughness requirement without obvious stripes and protrusions. Ultrasonic sandblasting allows the agglomerated sandblasting particles to be dispersed, which can improve the consistency of the surface roughness of the lead frame. Combining electroplating with ultrasonic sandblasting can increase the bonding force between the plastic encapsulation material and the lead frame surface, and improve the quality stability, performance and yield rate of the product.

[0027] In the electroplating process, the developed metal thin material is placed in the electroplating equipment for electroplating. Specifically, after the developed metal thin material is connected to the wire, it is placed in the electroplating solution of the electroplating equipment for electroplating, and then washed with clean water and dried. The process parameters of the electroplating process are determined according to factors such as the depth of the calendering indentation, the type of electroplated metal, the composition and concentration of the electroplating solution. In some embodiments, the electroplating time is 5 to 50 seconds, the electroplating temperature is 30 to 80°C, the coating thickness is less than 1 μm, and the coating thickness is determined according to the depth of the calendering lines of the metal thin material. Thus, the bonding force between the lead frame and the dry film, plastic encapsulation material, etc. is improved by chemical means, and the indentation defects of the calendered thin material of the lead frame raw material itself are reduced or concealed.

[0028] The process parameters of ultrasonic sandblasting are determined according to the roughness of the lead frame required for combination with the dry film and the plastic encapsulation material. In some embodiments, in the ultrasonic sandblasting process, the sandblasting equipment is any one of a dry sandblasting machine or a wet sandblasting machine, the sandblasting particles are made of corundum sand, the sandblasting particle size is 200 to 500 meshes, the sandblasting time is 10 to 100 seconds, the sandblasting depth is 0.05 to 0.2 μm, and the ultrasonic frequency is 10 to 100 kHz. If other process parameters are used, the roughness may be too low, the surface of the lead frame is too smooth, and the adhesion with the dry film and the plastic encapsulation material is insufficient; or the roughness is too high, the surface of the lead frame is visibly uneven, and the plastic encapsulation material expands and contracts during packaging, which is easy to cause warping or voids when encapsulating with the plastic encapsulation material, and the surface is too rough, which is not conducive to the lead frame transmitting electrical signals.

[0029] In the embodiment of the present invention, sandblasting and ultrasonic wave are performed simultaneously, which can effectively disperse the sand particles. After the sand particles hit the surface of the material, the consistency of the surface roughness is improved.

[0030] In the above-mentioned embodiment of the present invention, before electroplating, there are indentation defects caused by the calendering process on the surface of the lead frame raw material rolled thin material, and the electroplating is combined with ultrasonic sandblasting. The electroplating improves the bonding strength between the lead frame and the dry film and the plastic packaging material by chemical means, and reduces or conceals the indentation defects of the lead frame raw material rolled thin material itself. The ultrasonic sandblasting polishes the surface after electroplating by physical means, so that the pits and convex humps of the electroplating are processed, and the surface of the material after electroplating has a suitable roughness, and the roughness is not much different at each position of the material, thereby effectively improving the flatness and roughness consistency of the lead frame, and improving the calendering lines and the protrusions of the electroplating surface; after electroplating and ultrasonic sandblasting, the surface of the lead frame material has no defects such as calendering indentations, electroplating humps, and electroplating pits, which can effectively improve the bonding strength between the lead frame and materials such as the sensing film and the plastic packaging material, and improve the performance of the product.

[0031] In some embodiments, before the electroplating process, a discharge process and a development process are also included, and the development process is after the discharge process.

[0032] The unloading process includes placing the metal sheet coil processed by the previous exposure process into the unloading station. In some embodiments, the material of the metal sheet is any one of pure copper, pure gold, copper alloy, nickel alloy, stainless steel, titanium alloy, aluminum alloy and copper-based composite material; if the metal sheet is too thin, its conductivity is difficult to meet the requirements, and if it is too thick, it does not meet the packaging requirements of high-precision chips. Preferably, the thickness of the metal sheet is 0.01-0.2 mm to meet the requirements of making chips, semiconductors, and integrated circuits.

[0033] The developing process includes developing the plate-making pattern on the metal thin material with a developer, and then cleaning and drying it. The parameters of the developing process are determined according to factors such as the composition and thickness of the sensing film and the accuracy requirements of the plate-making pattern. Among them, the developer is any one or more of weak alkalis such as Na2CO3·10H2O, K2CO3 and copper sulfate, the developing time is 30 to 300 seconds, and the cleaning liquid is deionized water. In this way, the developer is used to clean the unexposed part and retain the part that undergoes polymerization reaction after exposure.

[0034] In some embodiments, after the ultrasonic sandblasting process, a first water washing process, a film stripping process, a second water washing process, a drying process, a material collecting process and a film coating process are sequentially included.

[0035] In the first water washing process, the metal thin material obtained by ultrasonic sandblasting is washed with water until no sand particles and sandblasting liquid remain on the surface. In some embodiments, the washing liquid is deionized water, and the washing time is 30 seconds to 600 seconds to remove the sand particles remaining on the surface.

[0036] In the film stripping process, the metal thin material after the first water washing is stripped, wherein the film stripped is the dry film (sensing film) remaining on the surface of the lead frame, that is, the dry film left after the development and undergoing the polymerization reaction, in preparation for the subsequent second dry film coating. In some embodiments, the film stripping liquid is potassium hydroxide, the film stripping temperature is 30 to 100° C., and the film stripping time is 100 to 600 seconds.

[0037] In the second washing process, the metal thin material after stripping is cleaned until there is no stripping liquid residue on the surface. In some embodiments, the washing time is 0.5 minutes to 5 minutes, and the washing liquid is deionized water, which can remove the stripping liquid residue until the pH of the liquid after washing tends to be neutral.

[0038] The drying temperature and time are mainly set according to factors such as the thickness of the metal sheet, the surface coating, and the wetting angle between water and the metal foil. In some embodiments, the washed metal sheet is dried in the drying process. The drying temperature is 30 to 120° C., the drying time is 0.5 to 100 minutes, and the surface of the metal sheet is dry and the coating is not discolored.

[0039] In the material collection process, the dried metal thin material is transported to the material collection station, and then the collected metal thin material is coated to obtain a lead frame product with a photosensitive film. In some embodiments, the coating process includes: adhering the photosensitive film to the surface of the metal thin material through a laminator, and then placing and fixing the product pattern to be produced on the outer surface of the photosensitive film to obtain a lead frame product with a photosensitive film; the coating process parameters are set considering factors such as the composition of the sensitive film and the adhesion to the lead frame, wherein: the material of the photosensitive film is any one or more of polyimide, photoresist, polyethylene and polyester film, and the thickness of the photosensitive film is 0.01 to 0.1 mm, thereby achieving secondary dry film coating without dry film shedding.

[0040] In the above-mentioned embodiment of the present invention, the metal thin material after the previous exposure is placed in the unloading station; then the plate-making pattern is developed on the metal thin material with a developer; then a layer of metal is electroplated on the surface of the metal thin material; then, sandblasting is performed under ultrasonic conditions, and then washed with water; then a film stripping agent is sprayed to strip the film, and the material is cleaned, dried, and collected; finally, a photosensitive film is pressed on the surface of the metal thin material to obtain the desired lead frame product. The above embodiment of the present invention combines electroplating with ultrasonic sandblasting, and polishes the surface of the coating layer by ultrasonic sandblasting, so that the stripes formed by the material rolling lines or the protrusions and sand holes caused by the particles on the surface of the coating layer are polished flat, so that the surface of the electroplated layer is flat, and the coating layer has a good surface state. Since the sandblasting is performed under an ultrasonic environment, the agglomeration of sand particles can be reduced, so that the dispersion of sand particles is greatly improved, and the situation that the surface roughness of the metal foil material in the existing process suddenly changes in the local area after sandblasting is solved, and the surface quality consistency of the lead frame can be improved, so that the surface of the lead frame has a suitable and consistent roughness, and the subsequent secondary coating (i.e., the coating process) and the demolding during the packaging of the plastic packaging material are effectively improved, thereby improving the quality stability and use performance of the lead frame, and having significant economic benefits. The method of the above embodiment of the present invention is simple in processing method, easy to mass produce, and the obtained product has a high yield rate and stable performance.

[0041] Continue to refer to Figure 1 In a specific embodiment, a surface treatment method of a lead frame comprises the following steps:

[0042] Step 1: Place the 0.1mm thick pure copper thin strip coil processed by the previous exposure process into the unloading station;

[0043] Step 2: Use Na2CO3·10H2O developer to develop the plate-making pattern on the pure copper strip obtained in the first step. The developing time is 180 seconds. After completion, the pure copper strip is washed with deionized water and dried.

[0044] Step 3: After the developed pure copper strip is connected to the wire, it is placed in the electroplating solution of the electroplating equipment to electroplate copper Cu, and the thickness of the copper plating layer is less than 1μm; the electroplating time is 15 seconds, and the electroplating temperature is 60°C. After the electroplating is completed, it is washed with deionized water and dried;

[0045] Step 4: sandblast the electroplated pure copper strip under ultrasonic conditions until the surface roughness reaches the preset requirements; the sandblasting equipment adopts a dry sandblasting machine, the sandblasting particles are white corundum sand, the sandblasting particle size is 400 mesh, the sandblasting time is 30 seconds, the sandblasting depth is 0.1μm, and the ultrasonic frequency is 20kHz;

[0046] Step 5: Wash the pure copper strip obtained in step 4 with deionized water for 500 seconds until no sand particles remain on the surface;

[0047] Step 6: After washing, the pure copper strip is stripped by spraying potassium hydroxide stripping solution at a stripping temperature of 70°C and a stripping time of 250 seconds;

[0048] Step 7: Use deionized water to clean the pure copper strip after film stripping for 3 minutes until there is no film stripping liquid left on the surface;

[0049] Step 8: Dry the washed pure copper strip at a temperature of 95°C for 1 minute.

[0050] Step 9: transport the dried pure copper strip to the receiving station;

[0051] Step 10: Use a laminator to adhere a 0.05 mm thick polyester photosensitive film to the surface of the pure copper strip obtained in step 9, and then place and fix the product pattern to be produced on the outer surface of the photosensitive film to obtain a lead frame product with a photosensitive film.

[0052] Compared with the physical sandblasting roughening process in the prior art, the lead frame product prepared by the above embodiment of the present invention has significantly improved adhesion to the plastic packaging material and dry film coverage area ratio, as shown in Table 1 below:

[0053] Table 1 Lead frame product performance comparison

[0054]

[0055] Another embodiment of the present invention provides a lead frame, which is manufactured using the above-mentioned surface treatment method of the lead frame.

[0056] The lead frame and the surface treatment method thereof in the above embodiment of the present invention adopts the method of pre-electroplating and then sandblasting in an ultrasonic environment, so that the subsequent secondary coating has a good adhesion effect. Compared with the prior art, the above embodiment of the present invention can improve the surface consistency of the lead frame, promote the close combination of the lead frame with the sensing film, the plastic packaging material, etc., so as to have higher adhesion and good stability, and the surface quality stability and performance of the lead frame product are significantly improved.

[0057] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various modifications or variations within the scope of the claims, which does not affect the essence of the present invention. The above preferred features can be used in any combination without conflicting with each other.

Claims

1. A surface treatment method for a lead frame, characterized in that: include: The ultrasonic sandblasting process is performed after the metal thin material electroplating process, and the ultrasonic sandblasting process includes sandblasting the electroplated metal thin material under ultrasonic conditions until the surface of the metal thin material reaches a preset roughness requirement.

2. The surface treatment method of the lead frame according to claim 1, characterized in that: In the electroplating process, the electroplating time is 5 to 50 seconds, the electroplating temperature is 30 to 80° C., and the plating layer thickness is less than 1 μm.

3. The surface treatment method of the lead frame according to claim 1, characterized in that: In the ultrasonic sandblasting process, the sandblasting particle size is 200-500 meshes, the sandblasting time is 10-100 seconds, the sandblasting depth is 0.05-0.2 μm, and the ultrasonic frequency is 10-100 kHz.

4. The surface treatment method of a lead frame according to claim 1, characterized in that: Before the electroplating process, a material discharge process and a development process are also included, and the development process is after the material discharge process.

5. The surface treatment method of a lead frame according to claim 4, characterized in that: The unloading process includes placing the metal thin material coil processed by the previous exposure process into the unloading station, wherein: the thickness of the metal thin material is 0.01-0.2 mm; The developing process includes developing the plate-making pattern on the metal thin material with a developer, wherein the developer is any one or more of Na2CO3·10H2O, K2CO3 and copper sulfate, and the developing time is 30 to 300 seconds.

6. The surface treatment method of a lead frame according to claim 1, characterized in that: After the ultrasonic sandblasting process, the first water washing process, the film stripping process, the second water washing process, the drying process, the material collecting process and the film coating process are sequentially included.

7. The surface treatment method of a lead frame according to claim 6, characterized in that: In the film stripping process, the film stripping liquid is potassium hydroxide, the film stripping temperature is 30 to 100° C., and the film stripping time is 100 to 600 seconds.

8. The surface treatment method of a lead frame according to claim 6, characterized in that: In the drying process, the drying temperature is 30 to 120° C., and the drying time is 0.5 to 100 minutes.

9. The surface treatment method of a lead frame according to claim 6, characterized in that: The laminating process includes: adhering a photosensitive film to the surface of the metal thin material by a laminating machine, and then placing and fixing a product pattern to be produced on the outer surface of the photosensitive film to obtain a lead frame product with a photosensitive film; Wherein: the material of the photosensitive film is any one or more of polyimide, photoresist, polyethylene and polyester film, and the thickness of the photosensitive film is 0.01-0.1 mm.

10. A lead frame, characterized in that: The lead frame is manufactured by the surface treatment method of any one of claims 1 to 9.

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