Method for manufacturing multilayer pre-plastic package structure of fine-engraved metal lead frame

Abstract

The invention relates to a manufacturing method of a multilayer pre-plastic package structure of a fine-engraved metal lead frame. The manufacturing method comprises the following steps: step 1, designing a pattern of the metal lead frame; 2, preparing a plate before manufacturing the metal lead frame; 3, positioning holes are manufactured before the metal lead frame is manufactured; 4, engraving a pattern on the back surface of the metal lead frame plate; 5, processing burrs on the back surface of the metal lead frame plate; sixthly, plastic packaging is conducted on the back face of the metal lead frame plate; 7, engraving a pattern on the front surface of the metal lead frame plate; 8, processing burrs on the front surface of the metal lead frame plate; ninthly, conducting plastic packaging on the front face of the metal lead frame plate; 10, electroplating the surface layer of the metal lead frame; and 11, cleaning the surface layer of the metal lead frame, baking, drying and packaging. The production efficiency and the manufacturing precision are improved, and the production and manufacturing cost and the environmental pollution are reduced.

Description

Technical Field

[0001] The invention relates to a method for manufacturing a finely engraved metal lead frame multi-layer pre-plastic packaging structure, belonging to the technical field of semiconductor packaging. Background Art

[0002] Metal lead frames used in existing semiconductor chip packaging are generally manufactured by two methods: stamping and chemical etching. The metal lead frame surface is then electroplated with a silver layer, a gold layer, or a nickel-palladium-gold layer over the entire surface or in a partial area.

[0003] During the chip packaging process, the semiconductor chip is installed on the metal lead frame formed by die punching or chemical etching → metal wire bonding → epoxy resin molding → plastic molding surface printing → metal lead frame surface tin layer electroplating → plastic molding cutting → electrical function test. According to the above semiconductor chip packaging process, it can be seen that the metal lead frame is a very important material for the entire chip packaging process and even the final chip electrical function test. It is one of the four main materials in semiconductor chip packaging (metal lead frame, conductive (non-conductive) glue, epoxy resin molding material, metal wire). It does not contain semiconductor chips and is the most expensive material among the four main materials.

[0004] The metal lead frame design and production methods currently available in the market all have more or less difficulty in production, and the difficulty of these production methods naturally causes a lot of hard defects. These hard defects also directly or indirectly cause troubles and threats to the semiconductor chip packaging production process and the reliability of the plastic package structure, which is an important issue that the industry is competing to improve.

[0005] Despite this, the industry is still only researching the die punching production methods and chemical etching production methods. The reason is that semiconductor chip packaging factories mainly focus on material application research and metal lead frame graphics design, while metal lead frame manufacturing factories conduct manufacturing method research and design and implement the manufacturing process based on the drawings required by the semiconductor chip packaging factory's design drawings and the required punching dies and etching masks.

[0006] In fact, metal lead frame manufacturers cannot truly understand the difficulties, real reasons, theories and solutions faced by semiconductor chip packaging factories in the chip packaging process, and semiconductor chip packaging factories cannot truly understand the difficulties, real reasons, theories and hard defects of metal lead frames in the production process due to production difficulties.

[0007] The following is a brief description of several defects caused by different manufacturing methods of metal lead frames:

[0008] 1. Punching die punching metal lead frame

[0009] The metal lead frame is mainly made by punching up and down with a metal tool, and it is currently the largest part of the metal lead frame used in semiconductor chip packaging. However, because the pattern of the metal lead frame is very complex, the design of the punching die and the production accuracy of the die are also quite complex and difficult.

[0010] It has the following defects and shortcomings:

[0011] A. Complex mold design: The design of punching molds requires too much manpower and time, and often leads to mistakes;

[0012] B. Difficulty in mold making: The upper and lower tools in the punching mold are almost all forming tools, which are very difficult and time-consuming to make;

[0013] C. High design and production costs: The design and production of punching dies are difficult, and the relative design and production costs are also very high;

[0014] D. High cost of punching equipment: The purchase cost of punching equipment used for punching dies is also quite high;

[0015] E. Threat of punching extrusion stress: During the punching process, the metal stress is directly formed due to the up and down extrusion of the tool, which causes failure and threat to the reliability of chip packaging;

[0016] F. Deformation of metal lead frame: The punching method of the punching die cannot produce convex points on the metal surface. At most, it can barely produce shallow small concave points on the metal surface. Otherwise, the surface of the metal lead frame will be squeezed and deformed (such as Figure 1 shown);

[0017] G. Epoxy resin packaging overflow: Because the punching die is punched or formed by up and down pressure, and because of the up and down extrusion, the punching section cannot be sharp but arc, which causes the overflow defect of epoxy resin plastic sealing in the chip packaging process (such as Figure 2 shown);

[0018] H. Inaccurate precision and uneven stress: The punching die needs to produce complex lead frame patterns, and the punching die needs a lot of steps to complete. Because the multi-step punching process will cause the movement of the metal lead frame, the deviation of the punching position accuracy and the imbalance of the burr size will cause the imbalance of metal stress (such as Figure 3 shown);

[0019] I. It is impossible to achieve high-density metal lead frames: Because the metal lead frame is punched by upper and lower cutters, it is impossible to achieve high-density pins inside the metal lead frame, otherwise the cutter is easy to break and the metal lead frame is scrapped. Therefore, basically a spacing of 1:2 or more of the plate depth-to-width ratio is used to ensure the safety of the upper and lower cutters as much as possible.

[0020] 2. Chemical Etching to Form Metal Lead Frame

[0021] Mainly, a dry or wet photoresist mask is coated on the surface of the metal plate, and photolithography is used to perform pattern conversion / exposure / development and etching to open windows for the parts that need to be etched by chemical agents. Then, chemical agents (such as cupric chloride or ferric chloride) are used to chemically etch the exposed metal surface area. After the chemical etching of the front and back of the metal plate is completed, the mask on the surface of the metal plate is removed to reveal the full appearance of the metal lead frame.

[0022] It has the following disadvantages and shortcomings:

[0023] A. Difficulty in drawing design: The design of etching mask patterns and silver layer electroplating patterns requires too much manpower and time, and it is necessary to obtain the data of etching factor after repeated actual chemical etching to truly determine the design drawing of the etching mask;

[0024] B. Repeated experiments are costly: Repeated experiments and design updates to obtain etching factors are time-consuming, material-consuming, labor-intensive, and equipment-intensive, and the relative costs are also very high;

[0025] C. Increased threat of harmful substances: Since the metal leads are made by chemical etching, many chemical solutions are used in the production process, which increases the cost of solving the pollution of harmful substances;

[0026] D. Difficult to control dimensional accuracy: Due to the use of chemical etching technology, the depth and depth plane of the semi-etching will change due to the concentration and ratio of the chemical agent, and it is impossible to control the accuracy and flatness (such as Figure 4 shown);

[0027] E. Chemical etching factors are difficult to control: Chemical etching methods often cause over-etching or under-etching precision problems and lead to scrapping due to the presence of more or less metal ions in the solution;

[0028] F. Unable to achieve high-density metal lead frame: Due to the chemical etching factor, the depth-to-width ratio of the etched metal material is at least 1:2, so the inner pins in the metal lead frame cannot achieve high-density line width and line spacing;

[0029] G. High production cost of chemical etching: The chemical etching process requires too much material, too long production time, difficult to control yield, complex environment, and high maintenance and cost of chemical solutions. Summary of the invention

[0030] The technical problem to be solved by the present invention is to provide a method for manufacturing a multi-layer pre-plastic packaging structure of a finely engraved metal lead frame in view of the above-mentioned prior art, which improves production efficiency and manufacturing accuracy, and reduces production costs and environmental pollution.

[0031] The technical solution adopted by the present invention to solve the above problem is: a method for manufacturing a finely engraved metal lead frame multi-layer pre-plastic packaging structure, the method comprising the following steps:

[0032] Step 1: Metal lead frame graphic design;

[0033] Step 2: Preparing the metal lead frame before making the plate;

[0034] Step 3: Pre-production of positioning holes for metal lead frame;

[0035] Step 4: Engraving the pattern on the back of the metal lead frame plate;

[0036] Step 5: Processing the burrs on the back of the metal lead frame plate;

[0037] Step 6: Plastic seal the back of the metal lead frame plate;

[0038] Step 7: The back of the metal lead frame is plastic-sealed and then baked for curing;

[0039] Step 8: Clean the plastic film on the back surface of the metal lead frame;

[0040] Step 9: Engraving the front graphics of the metal lead frame plate;

[0041] Step 10: Processing burrs on the front side of the metal lead frame plate;

[0042] Step 11: Plastic-sealing the front side of the metal lead frame plate;

[0043] Step 12: The front side of the metal lead frame is plastic-sealed and then baked for curing;

[0044] Step 13: Clean the plastic film on the front surface of the metal lead frame;

[0045] Step 14: electroplating the surface of the metal lead frame;

[0046] Step 15: Clean / bake and dry / package the surface of the metal lead frame.

[0047] A method for manufacturing a finely engraved metal lead frame multi-layer pre-plastic packaging structure, the method comprising the following steps:

[0048] Step 1: Metal lead frame graphic design;

[0049] Step 2: Preparing the metal lead frame before making the plate;

[0050] Step 3: Pre-plating the surface of the metal lead frame plate;

[0051] Step 4: Pre-production positioning holes for metal lead frame;

[0052] Step 5: Engraving the pattern on the back of the metal lead frame plate;

[0053] Step 6: Processing the burrs on the back of the metal lead frame plate;

[0054] Step 7: Plastic seal the back of the metal lead frame plate;

[0055] Step 8: The back of the metal lead frame is plastic-sealed and then baked for curing;

[0056] Step 9: Clean the plastic film on the back surface of the metal lead frame;

[0057] Step 10: Engraving the front graphics of the metal lead frame plate;

[0058] Step 11: Processing burrs on the front side of the metal lead frame plate;

[0059] Step 12: Plastic-sealing the front side of the metal lead frame plate;

[0060] Step 13: The front side of the metal lead frame is plastic-sealed and then baked for curing;

[0061] Step 14: Clean the plastic film on the front surface of the metal lead frame;

[0062] Step 15: Cleaning / baking and drying / packaging of the metal lead frame surface.

[0063] Optionally, in step one, graphics required for various functions of the metal lead frame of the semiconductor chip package are drawn according to the corresponding drawing software required by the CNC automatic engraving equipment. The graphics drawing is divided into the graphics drawing of various functions on the back side of the metal lead frame and the graphics drawing of various functions on the front side.

[0064] Optionally, the design drawing in step 1 is directly converted into an AutoCAM drawing for CNC dynamic engraving using the AutoCAD file format designed by the semiconductor chip packaging factory, or directly converted into a CNC program format for direct use without drawing.

[0065] Optionally, the positioning holes of the front plate of the metal lead frame are made by engraving with a metal carving knife, punching with a punching die, or corroding with a chemical etching method.

[0066] Optionally, use CNC metal engraving equipment with a metal engraving knife and metal lead frame graphics software to engrave the graphics and required depth on the back or front of the metal lead frame front plate.

[0067] Optionally, the method for treating the wire drawing burrs on the surface of the metal lead frame sheet is to use metal tool scraping treatment, surface grinder grinding treatment, chemical etching corrosion treatment, high-pressure sandblasting treatment or surface polishing.

[0068] Optionally, the metal engraving knife can scrape off the metal burrs generated during the engraving process while engraving the pattern and required depth on the back or front side of the metal lead frame front plate.

[0069] Optionally, the metal engraving knife includes a tool rod, a tool head is provided at the lower end of the tool rod, and a blade is provided at the lower end of the tool head; the tool head includes an upper connecting section and a lower engraving section; the bottom surface of the lower engraving section is designed to have an angle with the horizontal plane.

[0070] Optionally, an angle is designed between the left and right side surfaces of the lower carving section and the vertical plane; an angle is designed between the front side surface of the lower carving section and the vertical plane; an angle is designed between the left and right side surfaces of the blade and the vertical plane; an angle is designed between the front side surface of the blade and the vertical plane.

[0071] Compared with the prior art, the advantages of the present invention are:

[0072] 1. No need to redesign the metal lead frame design drawing: the precision milling and engraving process does not require the design of metal lead frame drawings separately. The metal lead frame AutoACD drawing files provided by the chip packaging factory can be directly converted into AutoCAM files or directly converted into CNC program formats, without wasting manpower and time on drawing.

[0073] 2. Low equipment purchase cost: The precision milling and engraving equipment is simple and high-precision, and the purchase cost is less than 50% of the punching equipment / mold and chemical etching equipment;

[0074] 3. No environmental pollution threat: The precision milling and engraving process does not require any chemical materials, only cooling water is needed for cooling, without environmental costs and pollution;

[0075] 4. Strengthen the bonding ability between chip and metal lead frame: The chip bearing base island bump is one of the important keys to solve the crack between chip and base island. The precision milling and engraving technology can easily carve out the microscopic bump height, which can fully maintain a certain ratio of bonding material and conductive material of the conductive glue (chip bonding material) under the chip, which is impossible to achieve in the punching mode and chemical etching mode;

[0076] 5. Easily engrave the concave points of the metal lead frame: The concave points on the back of the chip carrier base island are to strengthen the bonding ability between the epoxy resin (EMC) used for plastic packaging and the metal base island. The precision milling and engraving technology can easily do it, but the punching mold cannot impact it at all;

[0077] 6. Easily make hollowing of the metal lead frame base island: The hollowing of the chip carrier base island and the inner pins has two functions. One is to block the short circuit or leakage between the metal base island under the plastic package and the printed circuit board (PCB) circuit. The second is to make the epoxy resin used for plastic packaging better, which can increase the reliability of chip packaging. The precision milling and engraving technology can easily mill out the hollowing of the chip carrier base island and the inner pins, but the punching mold cannot punch out the same effect and structure;

[0078] 7. Easily make a metal lead frame with a large top and a small bottom structure: The metal base island and the inner pin end side structure in the metal lead frame are very important, and their main function is to increase the coating capacity of the epoxy resin used for plastic packaging. The precision milling and engraving technology can easily mill out the chip-bearing base island and the hollowing out below the inner pins, but it is difficult for the punching die to punch out structures of different sizes. Even if the structures of different sizes are punched out, they are formed by punching and extrusion. The residual stress of the different sizes formed by punching and extrusion is very serious, which is easy to affect the reliability of the chip packaging structure;

[0079] 8. No limitation on aspect ratio: The width of fine milling can be as small as 0.1mm and there is no limit on depth. It is very suitable for thick metals required for high currents and can easily achieve metal lead frames with higher density line widths and line spacings.

[0080] 9. If the surface of the metal lead frame is pre-plated with nickel-palladium-gold or metal silver, the semiconductor chip packaging factory can save the glue removal process after the chip is plastic-sealed and the tin layer electroplating process, and the costs of manpower, time, place, events, materials, quality and management. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] Figure 1 Schematic diagram of the deformation of the metal lead frame surface caused by the extrusion of metal surface pits.

[0082] Figure 2 Schematic diagram of epoxy resin molding overflow.

[0083] Figure 3 Schematic diagram of the deviation in punching position accuracy and the imbalance in burr size.

[0084] Figure 4 Schematic diagram showing that the depth and plane of half-etching cannot be controlled in chemical etching.

[0085] Figure 5 to Figure 11It is a schematic diagram of some processes of Example 1 of a method for manufacturing a multi-layer pre-plastic packaging structure of a finely engraved metal lead frame of the present invention.

[0086] Figures 12 to 18 It is a schematic diagram of some processes of Example 2 of a method for manufacturing a multi-layer pre-plastic packaging structure of a finely engraved metal lead frame of the present invention.

[0087] Fig.19 It is a schematic diagram of the structure of a metal engraving knife.

[0088] Fig. 20 for Fig.19 Side view of.

[0089] Fig.21 for Fig. 20 A partial enlarged view of .

[0090] in:

[0091] The knife bar 1, the knife head 2, the upper connecting section 21, the lower engraving section 22, the blade 3, the first arc section 4, the second arc section 5, the third arc section 6, the surface plastic sealing overflow 7, the small burr 8, and the large burr 9. DETAILED DESCRIPTION

[0092] The present invention is further described in detail below with reference to the accompanying drawings.

[0093] Embodiment 1: The metal lead frame is first engraved and then plated;

[0094] The present invention relates to a method for manufacturing a finely engraved metal lead frame multi-layer pre-plastic packaging structure, which comprises the following steps:

[0095] Step 1: Metal lead frame graphic design;

[0096] According to the corresponding drawing software required by the CNC automatic engraving equipment, the graphics required for each function of the metal lead frame of the semiconductor chip package are drawn. The graphics drawing is divided into the graphics drawing of each function on the back of the metal lead frame and the graphics drawing of each function on the front;

[0097] This design drawing can be directly converted into AutoCAM drawing for CNC dynamic engraving using the AutoCAD file format designed by the semiconductor chip packaging factory, or directly converted into CNC program format for direct use without having to draw it yourself.

[0098] Step 2: Preparing the metal lead frame before making the plate;

[0099] like Figure 5 As shown, according to the requirements of different semiconductor chip functions, a metal lead frame plate for semiconductor chip packaging is prepared;

[0100] The size of the metal lead frame sheet can be based on the size required by the packaging technology, such as strip or plate size;

[0101] The material of the front plate of the metal lead frame can be selected from iron alloy plate material, nickel-iron alloy plate material, pure copper plate material, copper alloy plate material, stainless steel plate material, etc. according to the different functions of the semiconductor chip.

[0102] Step 3: Pre-production of positioning holes for metal lead frame;

[0103] like Figure 6 As shown, after the metal lead frame is prepared, the plate positioning holes are first made. The purpose of making the plate positioning holes is to prepare for the positioning required for subsequent plate engraving and the positioning required for each process equipment during chip packaging;

[0104] The positioning holes of the front plate of the metal lead frame can be made by engraving with a metal carving knife, punching with a punching die, or corroding with a chemical etching method.

[0105] Step 4: Engraving the pattern on the back of the metal lead frame plate;

[0106] like Figure 7 As shown, the CNC metal engraving equipment is used with the required engraving knives of different sizes or special designs and the metal lead frame graphic software to engrave the graphics and required depth on the back of the metal lead frame front plate.

[0107] Step 5: Processing the burrs on the back of the metal lead frame plate;

[0108] After the engraving process on the back of the metal lead frame sheet is completed, due to the soft metal sheet and the passivation of the engraving tool, it is easy to produce wire drawing burrs on the surface of the metal lead frame sheet, and the surface of the metal lead frame sheet needs to be treated with wire drawing burrs;

[0109] The treatment methods for brushed burrs on the surface of metal lead frame plates can be metal tool scraping, surface grinding, chemical etching, high-pressure sandblasting, surface polishing, etc.

[0110] Step 6: Plastic seal the back of the metal lead frame plate;

[0111] like Figure 8 As shown, the material used for the plastic encapsulation of the back of the metal lead frame plate is basically epoxy resin (EMC), which has the following advantages: First, the non-metallic hollow area of ​​the metal lead frame is filled to fix the inner pins in the metal lead frame and the base island carrying the chip; second, the isolation between metals can be achieved to achieve the insulation effect of signals or power supply; third, when the chip is encapsulated in the plastic encapsulation process, there is a chance of isolating the plastic encapsulation material from overflowing.

[0112] Step 7: The back of the metal lead frame is plastic-sealed and then baked for curing;

[0113] After the epoxy resin (EMC) is molded on the metal lead frame sheet, the epoxy resin needs to be truly cured at high temperature for a long time and preferably in an oxygen-free environment to help the metal lead frame and the epoxy resin (EMC) truly bond together. The conditions and parameters for high-temperature, long-term, oxygen-free baking will vary depending on the characteristics of the epoxy resin (EMC) type.

[0114] Step 8: Clean the plastic film on the back surface of the metal lead frame;

[0115] The metal lead frame that has been encapsulated with epoxy resin (EMC) has more or less plastic encapsulation material overflowing on its surface and attached to the surface of the metal lead frame. These overflowing plastic encapsulation film is an organic substance and an insulating substance. If it is not cleaned, it will lead to the inability to electroplate the tin layer after chip encapsulation and the inability to solder the encapsulated chip body on the printed circuit board (PCB). Therefore, it is necessary to clean the plastic encapsulation film of the metal lead frame after epoxy resin encapsulation;

[0116] There are many ways to process the plastic film attached to the surface of the metal lead frame, such as direct removal with high-pressure water, softening with chemical solution + high-pressure water jet removal, grinding removal, polishing removal, laser scanning removal, sandblasting removal, etc.

[0117] Step 9: Engraving the front graphics of the metal lead frame plate;

[0118] like Fig. 9 As shown, CNC metal engraving equipment is used with metal engraving knives of different sizes and metal lead frame graphic software to engrave the graphics and required depth on the front side of the metal lead frame front plate. At this time, the metal lead frame front plate has formed a semi-finished metal lead frame.

[0119] Step 10: Processing burrs on the front side of the metal lead frame plate;

[0120] After the engraving process on the front of the metal lead frame sheet is completed, due to the soft metal sheet and the passivation of the engraving tool, it is easy to produce wire drawing burrs on the surface of the metal lead frame sheet, and the surface of the metal lead frame sheet needs to be treated with wire drawing burrs;

[0121] The treatment methods for brushed burrs on the surface of metal lead frame plates can be metal tool scraping, surface grinding, chemical etching, high-pressure sandblasting, surface polishing, etc.

[0122] Step 11: Plastic-sealing the front side of the metal lead frame plate;

[0123] like Fig.10 As shown, the material used for the plastic encapsulation of the back of the metal lead frame plate is basically epoxy resin (EMC), which has the following advantages: First, the non-metallic hollow area of ​​the metal lead frame is filled to fix the inner pins in the metal lead frame and the base island carrying the chip; second, the isolation between metals can be achieved to achieve the insulation effect of signals or power supply; third, during the plastic encapsulation in the post-film packaging process, there is a chance of isolating the plastic encapsulation material from overflowing.

[0124] Step 12: The front side of the metal lead frame is plastic-sealed and then baked for curing;

[0125] After the epoxy resin (EMC) is molded on the metal lead frame sheet, the epoxy resin needs to be truly cured at high temperature for a long time, preferably in an oxygen-free environment, to help the metal lead frame and the epoxy resin (EMC) to truly bond together. The conditions and parameters for high-temperature, long-term, oxygen-free baking will vary depending on the characteristics of the epoxy resin (EMC) type.

[0126] Step 13: Clean the plastic film on the front surface of the metal lead frame;

[0127] The metal lead frame that has been encapsulated with epoxy resin (EMC) has more or less plastic encapsulation material overflowing and adhering to the surface of the metal lead frame. These overflowing plastic encapsulation film is an organic substance and an insulating substance. If it is not cleaned, it will lead to the inability to electroplate the tin layer after chip encapsulation and the inability to solder the encapsulated chip body to the printed circuit board (PCB). Therefore, it is necessary to clean the plastic encapsulation film of the metal lead frame after epoxy resin encapsulation;

[0128] There are many ways to process the plastic film attached to the surface of the metal lead frame, such as direct removal with high-pressure water, softening with chemical solution + high-pressure water jet removal, grinding removal, polishing removal, laser scanning removal, sandblasting removal, etc.

[0129] Step 14: electroplating the surface of the metal lead frame;

[0130] like Fig.11 As shown, the surface electroplating of the metal lead frame can be divided into the electroplating of a separate local area on the front side of the metal lead frame, the electroplating of the whole area on the back side of the metal lead frame, and the electroplating of the whole area of ​​the front and back side of the metal lead frame at the same time. The purpose of the electroplating of the front side of the metal lead frame is different from that of the electroplating of the metal layer on the back side of the metal lead frame, as described in detail as follows:

[0131] A) Local electroplating on the front of the metal lead frame: The purpose of electroplating is mainly to implement metal wire bonding between the chip and the pins in the metal lead frame during the chip packaging process. The bonding process requires the metal wire to form an intermetallic compound (IMC) on the surface of the pins in the metal lead frame to achieve a good bonding ability between the metal wire material and the metal lead frame. The location of local electroplating is mainly related to the location of metal wire bonding, and the material of this electroplating layer is to help the metal wire and the pins in the metal lead frame to have a good intermetallic compound (IMC) after bonding;

[0132] The material for partial electroplating on the front side of the metal lead frame may be gold metal material, silver metal material, nickel-gold alloy metal material, nickel-palladium-gold alloy metal material, etc.

[0133] B) Full-area electroplating of the front and back of the metal lead frame: The full-area electroplating of the metal lead frame is divided into the electroplating of the metal material on the front of the metal lead frame and the electroplating of the metal material on the back of the metal lead frame;

[0134] B.1) The purpose and material of the electroplating on the front side of the metal lead frame are the same as those of the electroplating on the local area of ​​the front side of the metal lead frame mentioned above;

[0135] B.2) The purpose of electroplating the entire back surface of the metal lead frame is mainly because the bare lead frame material before electroplating is more susceptible to oxidation, rust, corrosion or contamination. After the surface of the metal lead frame is electroplated with a degradable metal layer, the oxidation, rust and corrosion of the original bare metal material can be prevented. However, the electroplated metal material of the entire back surface of the metal lead frame also needs to consider the metal tin used for soldering on the organic circuit board (PCB) after the chip packaging is completed;

[0136] The metal material used for the full-area metal material electroplating of the metal lead frame may be a nickel-gold alloy material, a nickel-palladium-gold alloy material, a metal pure tin material, a metal alloy tin material, and the like.

[0137] Step 15: Clean / bake and dry / package the surface of the metal lead frame.

[0138] After completing all the above steps, the metal lead frame is basically completed. However, considering the impact of transportation, storage environment and time, the metal lead frame may be contaminated, oxidized, rusted and corroded, which will seriously affect the subsequent chip packaging difficulties and product reliability and safety.

[0139] Therefore, after the above-mentioned metal lead frame fine milling and engraving is completed, the surface of the metal lead frame will be dried, sealed and packaged for cleaning and protection, and then it can be put into storage or shipped for transportation.

[0140] like Figure 19 to Figure 21As shown, the metal engraving knife used in step three, step four and step nine comprises a knife bar 1, a knife head 2 is arranged at the lower end of the knife bar 1, and a blade 3 is arranged at the lower end of the knife head 2;

[0141] The cutter head 2 comprises an upper connecting section 21 and a lower carving section 22;

[0142] The upper connecting section 21 is connected to the knife bar 1 through the first arc section 4;

[0143] The lower engraving section 22 is connected to the cutter head 2 via the second arc section 5;

[0144] The knife bar 1 is cylindrical;

[0145] The upper connecting section 21 is partially cylindrical, and the outer wall surface of the upper connecting section 21 is flush with the outer wall surface of the knife rod 1;

[0146] An angle is designed between the left and right side surfaces of the lower engraving section 22 and the vertical plane, and the angle range is 10° to 20°, preferably 15°;

[0147] An angle is designed between the front side surface of the lower engraving section 22 and the vertical surface, and the angle range is 10° to 20°, preferably 15°;

[0148] The rear side surface of the lower carving section 22 is flush with the rear side surface of the upper connecting section 21;

[0149] The bottom surface of the lower engraving section 22 is designed to have an angle with the horizontal plane, the angle range is 5° to 15°, preferably 10°;

[0150] The bottom surface and the front side surface of the lower engraving section 22 are connected via a third arc section 6;

[0151] An angle is designed between the left and right sides of the blade 3 and the vertical plane, and the angle range is 3° to 7°, preferably 5°;

[0152] An angle is designed between the front side of the blade 3 and the vertical plane, the angle range is 3° to 7°, preferably 5°;

[0153] The rear side surface of the blade 3 is flush with the rear side surface of the cutter head 2;

[0154] The bottom surface of the blade 3 is a horizontal surface;

[0155] The total length of the metal carving knife is 32 mm;

[0156] The length of the cutter head 2 is 8 mm;

[0157] The length of the blade 3 is 0.15 mm;

[0158] The radius of the first arc segment 4 is 1.6 mm, the radius of the second arc segment 5 is 0.2 mm, and the radius of the third arc segment 6 is 0.03 mm;

[0159] The above-mentioned super-hard and super-fine diameter metal engraving knife is used to perform fine milling and engraving on the front and back of the metal plate respectively, so that a metal lead frame can be quickly formed; and the above-mentioned specially designed metal forming engraving knife can scrape off the metal vertical burrs that may be generated in the engraving process of the metal lead frame (through the bottom surface of the knife head) while performing fine milling and engraving, so it can be used for burr processing on the back or front of the metal lead frame plate in steps five and ten.

[0160] Example 2: Metal lead frame is plated first and then engraved

[0161] Step 1: Metal lead frame graphic design;

[0162] According to the corresponding drawing software required by the CNC automatic engraving equipment, the graphics required for each function of the metal lead frame of the semiconductor chip package are drawn. The graphics drawing is divided into the graphics drawing of each function on the back of the metal lead frame and the graphics drawing of each function on the front;

[0163] This design drawing can be directly converted into AutoCAM drawing for CNC dynamic engraving using the AutoCAD file format designed by the semiconductor chip packaging factory, or directly converted into CNC program format for direct use without having to draw it yourself.

[0164] Step 2: Preparing the metal lead frame before making the plate;

[0165] like Fig.12 As shown, according to the requirements of different semiconductor chip functions, a metal lead frame plate for semiconductor chip packaging is prepared;

[0166] The size of the metal lead frame sheet can be based on the size required by the packaging technology, such as strip or plate size;

[0167] The material of the front plate of the metal lead frame can be selected from iron alloy plate material, nickel-iron alloy plate material, pure copper plate material, copper alloy plate material, stainless steel plate material, etc. according to the different functions of the semiconductor chip.

[0168] Step 3: Pre-plating the surface of the metal lead frame plate;

[0169] like Fig.13 As shown, the entire surface area of ​​the metal lead frame surface plate is pre-plated;

[0170] Step 4: Pre-production positioning holes for metal lead frame;

[0171] like Fig.14As shown, after the metal lead frame is pre-plated, the plate positioning holes are first made. The purpose of making the plate positioning holes is to prepare for the positioning required for subsequent plate engraving and the positioning required for each process equipment during chip packaging;

[0172] The positioning holes of the front plate of the metal lead frame can be made by engraving with a metal carving knife, punching with a punching die, or corroding with a chemical etching method.

[0173] Step 5: Engraving the pattern on the back of the metal lead frame plate;

[0174] like Fig.15 As shown, CNC metal engraving equipment is used with metal engraving knives of different sizes and metal lead frame graphic software to engrave the graphics and required depth on the back of the metal lead frame front plate.

[0175] Step 6: Processing the burrs on the back of the metal lead frame plate;

[0176] After the engraving process on the back of the metal lead frame sheet is completed, due to the soft metal sheet and the passivation of the engraving tool, it is easy to produce wire drawing burrs on the surface of the metal lead frame sheet, and the surface of the metal lead frame sheet needs to be treated with wire drawing burrs;

[0177] The treatment methods for brushed burrs on the surface of metal lead frame plates can be metal tool scraping, surface grinding, chemical etching, high-pressure sandblasting, surface polishing, etc.

[0178] Step 7: Plastic seal the back of the metal lead frame plate;

[0179] like Fig.16 As shown, the material used for plastic encapsulation of the back of the metal lead frame plate is basically epoxy resin (EMC), which has the following advantages: first, the non-metallic hollow area of ​​the metal lead frame is filled to fix the inner pins in the metal lead frame and the base island carrying the chip; second, the isolation between metals can be achieved to achieve the insulation effect of signals or power supply; third, when the chip is encapsulated in the plastic encapsulation process, there is a chance of isolating the plastic encapsulation material from overflowing.

[0180] Step 8: The back of the metal lead frame is plastic-sealed and then baked for curing;

[0181] After the epoxy resin (EMC) is molded on the metal lead frame sheet, the epoxy resin needs to be truly cured at high temperature for a long time, preferably in an oxygen-free environment, to help the metal lead frame and the epoxy resin (EMC) to truly bond together. The conditions and parameters for high-temperature, long-term, oxygen-free baking will vary depending on the characteristics of the epoxy resin (EMC) type.

[0182] Step 9: Clean the plastic film on the back surface of the metal lead frame;

[0183] The metal lead frame that has been encapsulated with epoxy resin (EMC) has more or less plastic encapsulation material overflowing and adhering to the surface of the metal lead frame. These overflowing plastic encapsulation film is an organic substance and an insulating substance. If it is not cleaned, it will lead to the inability to electroplate the tin layer after chip encapsulation and the inability to solder the encapsulated chip body to the printed circuit board (PCB). Therefore, it is necessary to clean the plastic encapsulation film of the metal lead frame after epoxy resin encapsulation;

[0184] There are many ways to process the plastic film attached to the surface of the metal lead frame, such as direct removal with high-pressure water, softening with chemical solution + high-pressure water jet removal, grinding removal, polishing removal, laser scanning removal, sandblasting removal, etc.

[0185] Step 10: Engraving the front graphics of the metal lead frame plate;

[0186] like Fig.17 As shown, CNC metal engraving equipment is used with metal engraving knives of different sizes and metal lead frame graphic software to engrave the graphics and required depth on the front side of the metal lead frame front plate. At this time, the metal lead frame front plate has formed a semi-finished metal lead frame.

[0187] Step 11: Processing burrs on the front side of the metal lead frame plate;

[0188] After the engraving process on the front of the metal lead frame sheet is completed, due to the soft metal sheet and the passivation of the engraving tool, it is easy to produce wire drawing burrs on the surface of the metal lead frame sheet, and the surface of the metal lead frame sheet needs to be treated with wire drawing burrs;

[0189] The treatment methods for brushed burrs on the surface of metal lead frame plates can be metal tool scraping, surface grinding, chemical etching, high-pressure sandblasting, surface polishing, etc.

[0190] Step 12: Plastic-sealing the front side of the metal lead frame plate;

[0191] like Fig.18 As shown, the material used for plastic encapsulation of the back of the metal lead frame plate is basically epoxy resin (EMC), which has the following advantages: first, the non-metallic hollow area of ​​the metal lead frame is filled to fix the inner pins in the metal lead frame and the base island carrying the chip; second, the isolation between metals can be achieved to achieve the insulation effect of signals or power supply; third, when the chip is encapsulated in the plastic encapsulation process, there is a chance of isolating the plastic encapsulation material from overflowing.

[0192] Step 13: The front side of the metal lead frame is plastic-sealed and then baked for curing;

[0193] After the epoxy resin (EMC) is molded on the metal lead frame sheet, the epoxy resin needs to be truly cured at high temperature for a long time, preferably in an oxygen-free environment, to help the metal lead frame and the epoxy resin (EMC) to truly bond together. The conditions and parameters for high-temperature, long-term, oxygen-free baking will vary depending on the characteristics of the epoxy resin (EMC) type.

[0194] Step 14: Clean the plastic film on the front surface of the metal lead frame;

[0195] The metal lead frame that has been encapsulated with epoxy resin (EMC) has more or less plastic encapsulation material overflowing and adhering to the surface of the metal lead frame. These overflowing plastic encapsulation film is an organic substance and an insulating substance. If it is not cleaned, it will lead to the inability to electroplate the tin layer after chip encapsulation and the inability to solder the encapsulated chip body to the printed circuit board (PCB). Therefore, it is necessary to clean the plastic encapsulation film of the metal lead frame after epoxy resin encapsulation;

[0196] There are many ways to process the plastic film attached to the surface of the metal lead frame, such as direct removal with high-pressure water, softening with chemical solution + high-pressure water jet removal, grinding removal, polishing removal, laser scanning removal, sandblasting removal, etc.

[0197] Step 15: Clean / bake and dry / package the surface of the metal lead frame.

[0198] After completing all the above steps, the metal lead frame is basically completed. However, considering the impact of transportation, storage environment and time, the metal lead frame may be contaminated, oxidized, rusted and corroded, which will seriously affect the subsequent chip packaging difficulties and product reliability and safety.

[0199] Therefore, after completing the above-mentioned metal lead frame milling, engraving and electroplating, the metal lead frame surface will be dried, sealed and packaged, etc., and then it can be put into storage or shipped.

[0200] In addition to the above embodiments, the present invention also includes other implementation modes. Any technical solutions formed by equivalent transformation or equivalent replacement should fall within the protection scope of the claims of the present invention.

Claims

1. A method for manufacturing a finely engraved metal lead frame multi-layer pre-plastic packaging structure, characterized in that The method comprises the following steps: Step 1: Metal lead frame graphic design; Step 2: Preparing the metal lead frame before making the plate; Step 3: Pre-production positioning holes for metal lead frame; Step 4: Engraving the pattern on the back of the metal lead frame plate; Step 5: Processing the burrs on the back of the metal lead frame plate; Step 6: Plastic seal the back of the metal lead frame plate; Step 7: The back of the metal lead frame is plastic-sealed and then baked for curing; Step 8: Clean the plastic film on the back surface of the metal lead frame; Step 9: Engraving the front graphics of the metal lead frame plate; Step 10: Processing burrs on the front side of the metal lead frame plate; Step 11: Plastic-sealing the front side of the metal lead frame plate; Step 12: The front side of the metal lead frame is plastic-sealed and then baked for curing; Step 13: Clean the plastic film on the front surface of the metal lead frame; Step 14: electroplating the surface of the metal lead frame; Step 15: Clean / bake and dry / package the surface of the metal lead frame.

2. A method for manufacturing a finely engraved metal lead frame multi-layer pre-plastic packaging structure, characterized in that The method comprises the following steps: Step 1: Metal lead frame graphic design; Step 2: Preparing the metal lead frame before making the plate; Step 3: Pre-plating the surface of the metal lead frame plate; Step 4: Pre-production positioning holes for metal lead frame; Step 5: Engraving the pattern on the back of the metal lead frame plate; Step 6: Processing the burrs on the back of the metal lead frame plate; Step 7: Plastic seal the back of the metal lead frame plate; Step 8: The back of the metal lead frame is plastic-sealed and then baked for curing; Step 9: Clean the plastic film on the back surface of the metal lead frame; Step 10: Engraving the front graphics of the metal lead frame plate; Step 11: Processing burrs on the front side of the metal lead frame plate; Step 12: Plastic-sealing the front side of the metal lead frame plate; Step 13: The front side of the metal lead frame is plastic-sealed and then baked for curing; Step 14: Clean the plastic film on the front surface of the metal lead frame; Step 15: Cleaning / baking and drying / packaging of the metal lead frame surface.

3. The method for manufacturing a finely engraved metal lead frame multi-layer pre-plastic packaging structure according to claim 1 or 2, characterized in that: In step 1, the graphics required for various functions of the metal lead frame of the semiconductor chip package are drawn according to the corresponding drawing software required by the CNC automatic engraving equipment. The graphics drawing is divided into the graphics drawing of various functions on the back side of the metal lead frame and the graphics drawing of various functions on the front side.

4. The method for manufacturing a finely engraved metal lead frame multi-layer pre-plastic packaging structure according to claim 1 or 2, characterized in that: In step 1, the design drawing is directly converted into the AutoCAD file format designed by the semiconductor chip packaging factory into the AutoCAM drawing file for CNC dynamic engraving or directly converted into the CNC program format for direct use without drawing.

5. The method for manufacturing a finely engraved metal lead frame multi-layer pre-plastic packaging structure according to claim 1 or 2, characterized in that: The positioning holes of the front plate of the metal lead frame are made by engraving with a metal carving knife, punching with a punching die, or corroding with a chemical etching method.

6. The method for manufacturing a finely engraved metal lead frame multi-layer pre-plastic packaging structure according to claim 1 or 2, characterized in that: Use CNC metal engraving equipment with metal engraving knives and metal lead frame graphics software to engrave the graphics and required depth on the back or front of the metal lead frame front plate.

7. The method for manufacturing a finely engraved metal lead frame multi-layer pre-plastic packaging structure according to claim 1 or 2, characterized in that: The methods for treating the brushed burrs on the surface of the metal lead frame sheet include scraping with metal tools, grinding with surface grinders, chemical etching and corrosion, high-pressure sandblasting or surface polishing.

8. The method for manufacturing a finely engraved metal lead frame multi-layer pre-plastic packaging structure according to claim 1 or 2, characterized in that: The metal engraving knife can engrave the pattern and required depth on the back or front of the metal lead frame front plate and at the same time scrape off the metal burrs generated during the engraving process.

9. The method for manufacturing a finely engraved metal lead frame multi-layer pre-plastic packaging structure according to claim 8, characterized in that: The metal carving knife comprises a knife bar, a knife head is arranged at the lower end of the knife bar, and a blade is arranged at the lower end of the knife head; the knife head comprises an upper connecting section and a lower carving section; the bottom surface of the lower carving section is designed to have an angle with a horizontal plane.

10. The method for manufacturing a finely engraved metal lead frame multi-layer pre-plastic packaging structure according to claim 9, characterized in that: An angle is designed between the left and right side surfaces of the lower carving section and the vertical surface; an angle is designed between the front side surface of the lower carving section and the vertical surface; an angle is designed between the left and right side surfaces of the blade and the vertical surface; an angle is designed between the front side surface of the blade and the vertical surface.

Images