Lead frame manufacturing process and lead frame

Abstract

This invention relates to the fabrication process and technical field of leadframes. The leadframe includes a design circuit and a positioning frame, with the bottom of the design circuit protruding laterally to form a bonding pad protrusion. The fabrication process includes: a first etching step, where, based on the design circuit of the leadframe, a partial etching is performed longitudinally from the top surface of the metal substrate, covering the area outside the design circuit (partial etching means not completely etched through); a filling step, where insulating plastic is filled into the partially etched area to form a positioning frame to position the design circuit; a second etching step, where longitudinal etching is performed from the bottom surface of the metal substrate, etching through the partially etched area from the first etching step; the etching area from the bottom surface of the metal substrate to the corresponding area is smaller than the etching area from the top surface of the metal substrate to the corresponding area, so that the bottom of the design circuit protrudes laterally to form the bonding pad protrusion. The bonding pad protrusion supports the positioning frame on the bottom surface of the positioning frame, preventing the positioning frame from shifting downwards under injection molding pressure, thus improving chip reliability.

Description

Technical Field

[0001] This invention relates to the field of chip packaging technology, and more specifically to the field of lead frame technology. Background Technology

[0002] Semiconductor packaging is the manufacturing process of encapsulating dies (also known as wafers) into chips. In this manufacturing process, the lead frame is one of the most important components.

[0003] Diodes are typically very small, but they have many ports that need to be electrically connected to external circuits. Due to the small size of the die, these ports cannot be directly electrically connected to external circuits. Therefore, when packaging the die, lead frames are used to bring out the ports that need to be electrically connected to external circuits so that the packaged chip can be directly electrically connected to external circuits.

[0004] Chinese patent ZL201710677235.8 discloses a leadframe manufacturing process. This process involves forming the designed circuitry after two etching steps. The designed circuitry has the same lateral width on both the top and bottom surfaces, and its sides are flat (see part d in Figure 3 of the patent specification). During chip packaging, after attaching the die and bonding wires, injection molding is required to form a protective shell for the die and wires. Injection pressure is applied from top to bottom to the positioning frame. The positioning frame only engages with the flat side of the designed circuitry, resulting in poor bonding strength. Under the injection pressure, it may shift downwards, reducing the reliability of the chip product. If the positioning frame shifts downwards and becomes flush with the outer leads, the outer leads will not protrude downwards. In subsequent SMT processes, the outer leads are less prone to solder creep, further reducing soldering reliability. While this leadframe can be applied to most IC products, it still has some reliability shortcomings for automotive products with high packaging reliability requirements. Summary of the Invention

[0005] In view of this, the lead frame manufacturing process and lead frame provided by the present invention result in chips with high reliability.

[0006] To achieve the above objectives, the present invention provides the following technical solutions.

[0007] 1. The lead frame manufacturing process includes the following steps:

[0008] First etching: According to the design line of the lead frame, the area outside the design line is partially etched longitudinally from the top surface of the metal substrate. Partial etching means that it is not etched through.

[0009] Filling: Insulating plastic is filled into the semi-etched area to form a positioning frame to position the designed circuit;

[0010] Second etching: Vertical etching from the bottom surface of the metal substrate, etching through the half-etched positions in the first etching step;

[0011] The etching area from the bottom of the metal substrate to the corresponding area is smaller than the etching area from the top of the metal substrate to the corresponding area, so that the bottom of the designed circuit protrudes laterally to form a glue-on horizontal protrusion.

[0012] When leadframes are used for chip packaging, after the die is attached to the top surface and wires are bonded, molding is performed. Molding is the process of injection molding a shell for the chip from the top surface to protect the die and the wire bonding lines. During the injection molding process, there is injection pressure, which is applied downwards to the positioning frame. The horizontal width of the designed circuit on the bottom surface is greater than its horizontal width on the top surface, forming a glue-fastening convex shape on the bottom. The longitudinal cross-section of the designed circuit is similar to an inverted T shape. The glue-fastening convex shape supports the positioning frame on the bottom surface, so that the positioning frame will not shift downwards when subjected to the above injection pressure. This improves the reliability of the chip and also prevents the positioning frame from being flush with the part of the designed circuit on the bottom surface. The part of the bottom surface of the designed circuit is the outer foot, which protrudes downwards. In subsequent SMT processes, the outer foot is more prone to solder creep, resulting in higher soldering reliability.

[0013] 2. Based on technical solution 1, the design circuit includes pins and a base for mounting the chip. After the glue filling step, a first, upward-protruding, conductive glue-locking protrusion is formed on the top surface of the pins. This first glue-locking protrusion extends laterally to hold the positioning frame. After the glue filling forms the positioning frame, the top surface is usually polished to remove excess glue, thus flattening the top surface. When the die is mounted on the top surface and wire bonded, and then encapsulated, the bonding surface between the encapsulated shell and the top surface of the lead frame is flat, resulting in poor adhesion and easy lateral displacement, reducing chip reliability. By forming the first glue-locking protrusion in a portion of the top surface of the design circuit (i.e., the inner pin), the first glue-locking protrusion is inserted into the encapsulated shell. The bonding surface between the shell and the top surface of the lead frame is not flat but has unevenness, resulting in stronger adhesion and less lateral displacement of the shell, thus improving chip reliability.

[0014] 3. Based on technical solution 2, the longitudinal thickness of the first adhesive protrusion is 5μm-150μm, and the lateral width extending laterally to the top of the positioning frame is 5μm-200μm.

[0015] 4. Based on technical solution 2, the first adhesive protrusion is made by electroplating. Electroplating is an essential process in the manufacture of the lead frame. Using electroplating to make the first adhesive protrusion can save steps and eliminate the need for additional design processes.

[0016] 5. Based on technical solution 4, copper or nickel is electroplated to form the first adhesive protrusion, and then silver or nickel-palladium-gold is electroplated on the first adhesive protrusion to form the bonding wire surface. The inner leads typically require electroplating to form the bonding wire surface. The bonding wire surface is usually quite thin and cannot serve as the first adhesive protrusion. Furthermore, the bonding wire surface usually requires precious metals such as silver or nickel-palladium-gold for electroplating. If a thicker bonding wire surface were used to simultaneously serve as the first adhesive protrusion, the cost would be high. Therefore, copper or nickel is electroplated first to form the first adhesive protrusion, and then silver or nickel-palladium-gold is electroplated on top to form the bonding wire surface, thereby reducing costs.

[0017] 6. Based on technical solution 1, in the first etching step, a portion of the top surface of the metal substrate, excluding the designed circuitry, is shielded. This portion is located directly above the adhesive bonding convexity. During etching, this portion is longitudinally etched away to form a second, upward-protruding adhesive bonding convexity on the adhesive bonding convexity. After the adhesive is filled to form the positioning frame, the second adhesive bonding convexity is inserted into the positioning frame, further increasing the bonding force between the positioning frame and the designed circuitry, making it less prone to loosening or breakage, and improving the reliability of the packaged chip.

[0018] 7. Based on technical solution 1, in the first etching step, the etching depth of the semi-etching is 1 / 2 to 4 / 5 of the thickness of the metal substrate.

[0019] 8. Lead frame, made using the manufacturing process described in technical solutions 1-7, including design circuit and positioning frame. The bottom of the design circuit protrudes horizontally to form a snap-on horizontal protrusion, so as to lock the bottom surface of the positioning frame and prevent the positioning frame from moving downward.

[0020] 9. Based on technical solution 8, the design circuit includes pins and a base for attaching the chip. The top surface of the pins is provided with an upwardly protruding and conductive first adhesive protrusion, which extends laterally to hold the positioning frame.

[0021] 10. Based on technical solution 8, the snap-on horizontal protrusion is provided with a second snap-on protrusion that protrudes upward and is inserted into the positioning bracket. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the lead frame structure of the present invention.

[0023] Figure 2 For Figure 1 The diagram shows the AA section in each step of the lead frame manufacturing process in this embodiment.

[0024] The reference numerals in the figures include:

[0025] Base 1, pin 2, inner pin 21, first adhesive protrusion 211, bonding surface 212, outer pin 22, adhesive horizontal protrusion 221, second adhesive protrusion 222, metal substrate 3, positioning frame 4, photosensitive film 5. Detailed Implementation

[0026] The invention will be described in detail below with reference to specific embodiments.

[0027] like Figure 1 and Figure 2 As shown in part f, the lead frame of this embodiment includes a base 1, pins 2, and a positioning frame 4. During the fabrication of the lead frame, the base 1 and pins 2 are collectively referred to as the design circuit. The base 1 and each pin 2 are fixed together by the positioning frame 4, their relative positions are determined, and there is no electrical connection between them. After the chip is packaged, it is not necessary to cut off the electrical connection between the base 1 and each pin 2. Figure 2 As shown in part f, the top and bottom of pin 2 are inner pin 21 and outer pin 22, respectively. The outer pin 22 protrudes laterally to form a glue-attaching horizontal protrusion 221. The base 1 also has a similar glue-attaching horizontal protrusion 221. The cross-sectional shape of the base 1 and pin 2 is similar to an inverted T-shape. The glue-attaching horizontal protrusion 221 is stuck on the bottom surface of the positioning frame 4 so that the positioning frame 4 will not shift downward when subjected to the injection pressure during the subsequent chip packaging process. This improves the reliability of the chip on the one hand, and on the other hand, the positioning frame 4 will not be flush with the outer pin 22 on the bottom surface. The outer pin 22 protrudes downward, and in the subsequent SMT process, the outer pin 22 is more likely to form solder crawling, resulting in higher soldering reliability.

[0028] After the adhesive filler forms the positioning frame 4, the top surface is usually polished to remove excess adhesive. This results in a flat top surface. When the die is attached to the top surface and wire bonded, followed by molding, the interface between the molding compound and the top surface of the lead frame is flat, leading to poor adhesion and lateral displacement, which reduces chip reliability. Figure 2 As shown in sections d and f, the top surface of the inner pin 21 is formed by two electroplating processes to create a first adhesive protrusion 211 and a bonding wire surface 212. The first adhesive protrusion 211 extends laterally to hold the positioning bracket. The first adhesive protrusion 211 is made of copper or nickel plating, while the bonding wire surface 212 is made of precious metals such as silver or nickel-palladium-gold plating. During the subsequent chip packaging process, the first adhesive protrusion 211 and the bonding wire surface 212 are inserted into the encapsulated shell. The mating surface between the shell and the top surface of the lead frame is not flat but has unevenness, resulting in a stronger bonding force and preventing lateral displacement of the shell, thus improving the reliability of the chip.

[0029] like Figure 2 As shown in parts e and f, the adhesive-coating convex 221 has an upwardly protruding second adhesive-coating protrusion 222. After the adhesive is filled to form the positioning frame 4, the second adhesive-coating protrusion 222 is inserted into the positioning frame 4, which can further increase the bonding force between the positioning frame 4 and the designed circuit, making it less prone to loosening or breakage, and improving the reliability of the packaged chip.

[0030] Figure 2 Part f shows a cross-sectional view of the finished lead frame of this embodiment.

[0031] like Figure 2 As shown, the lead frame manufacturing process of this embodiment includes the following steps:

[0032] Top surface exposure and development. For example... Figure 2 As shown in part a, photosensitive films 5 are attached to the top and bottom surfaces of the metal substrate 3. Then, according to the designed circuit, only the top surface is exposed and developed to form a portion that blocks the designed circuit on the top surface, and a portion adjacent to this portion is also blocked. The top surface is the surface on which the grains are attached.

[0033] First etching. (As shown) Figure 2 As shown in part b, a partial etching is performed longitudinally from the top surface of the metal substrate 3. Partial etching means that the etching is not completely etched through. In this embodiment, the etching depth of the partial etching is 1 / 2 to 4 / 5 of the thickness of the metal substrate. The design lines such as pin 2 and base 1 are not etched. The top of pin 2 is the inner foot 21. The shielding formed in a part of the area next to the design lines is laterally etched away during this etching process. Therefore, an upward protrusion is formed at the corresponding position at the bottom of the groove formed by etching. These protrusions are the second adhesive protrusions 222.

[0034] Filling with adhesive. For example... Figure 2 As shown in section c, insulating plastic is filled into the semi-etched area to form a positioning frame 4 to position the base 1 and the pin 2. A second adhesive protrusion 222 is inserted into the positioning frame 4. After the positioning frame 4 is formed by filling with adhesive, the top surface is polished to remove excess adhesive and other impurities.

[0035] Double electroplating. For example... Figure 2 As shown in section d, the top surface of the inner foot 21 is electroplated twice. The first electroplating is copper or nickel to form the first snap-on protrusion 211. The longitudinal thickness of the first snap-on protrusion 211 is 5μm-150μm. Electroplating is performed on the ground surface. As the electroplating thickness increases, the plating layer also grows laterally, causing the first snap-on protrusion 211 to extend laterally and lock the positioning frame 4. The lateral width extending laterally above the positioning frame is 5μm-200μm. Silver or nickel-palladium-gold is then electroplated on the first snap-on protrusion 211 to form the bonding surface 212. The inner foot 21 usually needs to be electroplated to form the bonding surface 212. The thickness of the bonding surface 212 is usually relatively thin and cannot serve as the first snap-on protrusion 211. Moreover, the bonding surface 212 usually needs to be formed by electroplating with precious metals such as silver or nickel-palladium-gold. If a thicker bonding surface 212 is electroplated to simultaneously serve as the first snap-on protrusion 211, the cost will be high. Therefore, copper or nickel is first electroplated to form the first adhesive protrusion 211, and then silver or nickel-palladium-gold is electroplated on it to form the solder wire surface 212, thereby reducing costs.

[0036] The bottom surface is exposed and developed. For example... Figure 2 As shown in section e, the bottom surface is developed and exposed according to the designed circuit.

[0037] Second etching. (As shown) Figure 2As shown in part f, longitudinal etching is performed from the bottom surface of the metal substrate 3, etching through the half-etched position in the first etching step, so that the bottom of the lead forms an outer foot 22. The etching area of ​​this etching is smaller than the etching area of ​​the first etching. Therefore, the width of the outer foot 22 in the horizontal direction is greater than the width of the inner foot 21 in the horizontal direction. The width of the bottom of the base 1 in the horizontal direction is greater than the width of the top of the base 1 in the horizontal direction. The outer foot 22 and the bottom of the base 1 both protrude horizontally to form a glue-fastening horizontal protrusion 221.

[0038] It should be noted that the process disclosed in Chinese Patent No. ZL201710677235.8 can also be used, which involves first electroplating to form the first adhesive protrusion 211 and then performing the first etching.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions created by the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions created by the present invention without departing from the essence and scope of the technical solutions created by the present invention.

Claims

1. The lead frame manufacturing process, characterized by: Includes the following steps: First etching: According to the design line of the lead frame, the area outside the design line is partially etched longitudinally from the top surface of the metal substrate. Partial etching means that it is not etched through. Filling: Insulating plastic is filled into the semi-etched area to form a positioning frame to position the designed circuit; Second etching: Vertical etching from the bottom surface of the metal substrate, etching through the half-etched positions in the first etching step; The etching area from the bottom of the metal substrate to the corresponding region is smaller than the etching area from the top of the metal substrate to the corresponding region, so that the bottom of the designed circuit bulges laterally to form a bonding pad bulge. In the first etching step, a portion of the metal substrate top surface, excluding the designed circuitry, is covered. This portion is located directly above the adhesive bonding convexity. During etching, this portion is longitudinally etched off to form an upward-protruding second adhesive bonding convexity on the adhesive bonding convexity.

2. The lead frame manufacturing process as described in claim 1, characterized in that, The design circuit includes pins and a base for attaching the chip. After the glue filling step, a first glue-attaching protrusion that is upwardly raised and conductive is formed on the top surface of the pin. The first glue-attaching protrusion extends laterally to hold the positioning frame.

3. The lead frame manufacturing process as described in claim 2, characterized in that, The longitudinal thickness of the first adhesive protrusion is 5μm-150μm, and the lateral width extending laterally to the top of the positioning frame is 5μm-200μm.

4. The lead frame manufacturing process as described in claim 2, characterized in that, The first adhesive protrusion is made using an electroplating process.

5. The lead frame manufacturing process as described in claim 4, characterized in that, Electroplating copper or nickel forms the first adhesive protrusion, and then electroplating silver or nickel-palladium-gold on the first adhesive protrusion forms the solder wire surface.

6. The lead frame manufacturing process as described in claim 1, characterized in that, In the first etching step, the etching depth of the semi-etch is 1 / 2 to 4 / 5 of the thickness of the metal substrate.

7. A lead frame, characterized in that, Made using the manufacturing process described in any one of claims 1-6, the product includes a design circuit and a positioning frame, wherein the bottom of the design circuit protrudes laterally to form a snap-on horizontal protrusion to hold the bottom surface of the positioning frame in place and prevent the positioning frame from moving downward.

8. The lead frame as described in claim 7, characterized in that, The design circuit includes pins and a base for attaching the chip. The top surface of the pins has an upwardly protruding and conductive first adhesive protrusion that extends laterally to hold the positioning frame.

9. The lead frame as described in claim 7, characterized in that, The snap-on horizontal protrusion is provided with a second snap-on protrusion that protrudes upward and is inserted into the positioning bracket.

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