Lead frame structure of special-shaped high radiating fin and corresponding chip packaging method

Abstract

The invention discloses a lead frame structure of a special-shaped high radiating fin, which enables a lead frame to have high radiating performance so as to be adaptive to a high-reliability product and ensure the reliable work of the product. The packaging structure comprises a frame body, the frame body is of a rectangular structure, a plurality of packaging units are arranged in the area of the frame body in an array mode, each packaging unit comprises a packaging area structure and a cooling fin, the cooling fin is a thick fin body, and thin pins are arranged at the two ends, corresponding to the length direction of the cooling fin, of the packaging area structure. The inner convex parts of the thin pins are connected with the upper surfaces of the two ends of the cooling fin in the length direction through laser welding, and a chip is placed on the upper surface of the cooling fin. The invention further provides a chip packaging method adopting the lead frame structure.

Description

Technical Field

[0001] The invention relates to the technical field of chip packaging, in particular to a lead frame structure of a special-shaped high heat sink. The invention also provides a chip packaging method using the lead frame structure. Background Art

[0002] The traditional packaging of plastic encapsulation compound + lead frame is widely used in various fields because of its low price. With the iterative upgrade of packaging materials, the packaging capacity of traditional products has been greatly improved, and the product reliability has also improved accordingly. For some high-reliability products, they have also begun to gradually shift from high-end packaging to traditional packaging of plastic encapsulation compound + lead frame. However, due to the high heat dissipation requirements of high-reliability products, the existing lead frame structure cannot meet the heat dissipation performance requirements of the products. For this reason, it is urgently necessary to develop a reliable lead frame with high heat dissipation performance. Summary of the invention

[0003] In view of the above problems, the present invention provides a lead frame structure with a special-shaped high heat sink, which enables the lead frame to have high heat dissipation performance, thereby being able to adapt to high-reliability products and ensure reliable operation of the products.

[0004] A lead frame structure for a special-shaped high heat sink, characterized in that it includes a frame body, the frame body is a rectangular structure, a plurality of packaging units are arrayed in the surface area of ​​the frame body, each packaging unit includes a packaging area structure and a heat sink, the heat sink is a thick sheet body, the packaging area structure is provided with thin pins at both ends of the heat sink in the length direction, the inner convex part of the thin pin is connected to the upper surface of the two ends of the heat sink in the length direction by laser welding, and a chip is placed on the upper surface of the heat sink.

[0005] It is further characterized by:

[0006] The connection between the heat sink and the thin pin is a π-shaped welding structure, and the welding points are all located inside the surface area of ​​the heat sink, which reduces the length of the bonding wire, shortens the current and signal transmission distance, reduces dielectric loss, and improves electrical performance and product reliability;

[0007] The thickness of the heat sink is 1-1.25 mm, the main body material of the heat sink is KFC, and the surface of the heat sink is fully silver-plated;

[0008] The upper surface of the heat sink is provided with heat sink front locking grooves on both sides in the width direction, which are used to enhance the combination of the base island and the plastic packaging material;

[0009] The upper surface of the heat sink is also provided with a plurality of dimples, and the positions of the dimples can be flexibly adjusted according to product requirements to enhance the bonding between the front side of the base island and the plastic packaging material;

[0010] The back of the heat sink is provided with a back locking step with a concave edge, and the back locking step is used to enhance the bonding between the heat sink and the back of the plastic packaging material;

[0011] The packaging area mechanism also includes inner pins and outer pins arranged corresponding to the number of chips, and the packaging area mechanism also includes inner pin locking holes arranged inside and outside corresponding to the inner pins, and the inner pin locking holes enable the inner pins and the plastic packaging material to be reliably combined.

[0012] A chip packaging method using a lead frame structure with a special-shaped high heat sink, characterized in that it comprises the following steps:

[0013] S1, dicing process, thinning the wafer and then dicing it to form corresponding chips;

[0014] S2, core mounting process, by which the chip is placed at the corresponding position on the upper surface of the heat sink, and glue is applied to complete the chip position curing;

[0015] S3, pressure welding and dispensing process, connect the chip with the corresponding inner pins, when the chips need to be connected, connect them through gold wire;

[0016] S4, a plastic encapsulation process, plastic encapsulating the base island of each package unit on the lead frame;

[0017] S5, tinning process, tinning the lead frame of the package through an automatic tinning line;

[0018] S6, printing process, printing the trademark on the surface of the plastic package;

[0019] S7, cutting and separating the ribs, cutting off the middle rib connecting rod connected to the lead frame to obtain an independent packaging structure.

[0020] After adopting the above technical solution, a laser welding process is used on the lead frame to assemble the heat sink to the base island area of ​​the lead frame. Compared with the traditional lead frame manufacturing method, this technology has a smaller heat affected zone, smaller thermal deformation, good welding quality, and no special environmental requirements. At the same time, for the high reliability and high heat dissipation characteristics of the product, the lead frame adopts a thick heat sink and thin pin connection method. The material uses high thermal conductivity material KFC. The heat sink is exposed to ensure good heat dissipation performance. High thermal conductivity fully sintered silver is used between the chip and the lead frame to meet the heat dissipation capacity ≥160W / mk, which solves the problems of good electrical conductivity and high heat dissipation. It enables the lead frame to have high heat dissipation performance, so that it can adapt to high reliability products and ensure reliable operation of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a top view schematic diagram of a lead frame corresponding to the present invention;

[0022] Figure 2 For the present invention Figure 1 A schematic diagram of a local enlarged structure;

[0023] Figure 3 for Figure 2 Schematic diagram of the structure after removing the heat sink;

[0024] Figure 4 A side view of the welding connection between the heat sink and the frame body of the present invention;

[0025] Figure 5 It is a front plan view of the heat sink of the present invention;

[0026] Figure 6 A schematic top view of a chip after bonding and connection using the lead frame mechanism of the present invention;

[0027] Figure 7 It is a front view of the packaging structure of a specific embodiment of the present invention;

[0028] Figure 8 A side view of a packaging structure of a specific embodiment of the present invention;

[0029] Fig. 9 A top view of a packaging structure according to a specific embodiment of the present invention;

[0030] Fig.10 The three-stage baking curve of sintered silver;

[0031] Fig.11 This is the baking curve of the five stages of sintering silver;

[0032] The names corresponding to the serial numbers in the figure are as follows:

[0033] Input line 1, BSOB line 2, output line 3;

[0034] Frame body 10, packaging unit 20, frame positioning hole 21, flow channel groove 22, PIN1 identification hole 23, packaging area structure 30, thin pin 31, inner pin 32, inner pin locking hole 321, outer pin 33, glue inlet 34, stabilizing reinforcement rib 35, heat sink 40, front locking groove 41, Dimple 42, back locking step 43. DETAILED DESCRIPTION

[0035] A lead frame structure with a special-shaped high heat sink, see Figure 1-Figure 5It includes a frame body 10, which is a rectangular structure. A plurality of packaging units 20 are arrayed in the surface area of ​​the frame body 10. Each packaging unit 20 includes a packaging area structure 30 and a heat sink 40. The heat sink 40 is a thick sheet body. The packaging area structure 30 is provided with thin pins 31 at both ends of the heat sink 40 in the length direction. The inner convex part of the thin pin 31 is connected to the upper surface of the two ends of the heat sink 40 in the length direction by laser welding. The upper surface of the heat sink 30 is used to place the chip.

[0036] In specific implementation, the connection between the heat sink 40 and the thin pin 31 is a π-shaped welding structure, and the welding points are all located inside the surface area of ​​the heat sink 40, which reduces the length of the bonding wire, shortens the current and signal transmission distance, reduces dielectric loss, and improves electrical performance and product reliability.

[0037] In a specific embodiment, the thickness of the heat sink 40 is 1-1.25 mm, the body material of the heat sink 40 is KFC, and the surface of the heat sink 40 is fully silver-plated;

[0038] The upper surface of the heat sink 40 is provided with front locking grooves 41 on both sides in the width direction. The front locking grooves 41 are concave V-grooves with an angle of 60°, a length of 10 mm, and a depth of 0.05-0.1 mm. The front locking grooves 41 are used to enhance the bonding between the base island and the plastic packaging material.

[0039] Several Dimple 42 are also arranged on the upper surface of the heat sink 40. The position of Dimple 42 can be flexibly adjusted according to product requirements. Dimple is designed to punch square patterns at different angles twice, with a length of 0.3mm and a depth of 0.2mm. Dimple 42 enhances the bonding between the front side of the base island and the plastic packaging material.

[0040] The back side of the heat sink 40 is provided with a back side locking step 43 with a concave edge. The back side locking step 43 is obtained by stamping and has a design size of 0.3 mm×0.3 mm. The back side locking step 43 is used to enhance the bonding between the heat sink and the back side of the plastic packaging material.

[0041] In a specific embodiment, the thick heat sink 40 is made of KFC, with a hardness (HV): 100-140, and is obtained by stamping. The heat sink needs to be fully silver-plated with a silver plating layer thickness of 2.5-7μm, and the thin pin 31 welded to the heat sink 40 is made of A194F.H, with a silver plating layer thickness of 2.5-7μm; the heat sink 40 and the thin pin 31 are connected by laser welding, with a maximum laser output power of 1500W, a modulation frequency of 500HZ, a wavelength of 1070nm, a welding speed of 2500m / s, a welding power of 500W, a push-pull force test AVG>8Kg, a solder joint diameter of 0.3mm-0.6mmMax, which can be adjusted, a solder joint height of 0.01mmMax, a parallelism of 0.025mm, a flatness of 0.03Max, a solder joint accuracy of 0.01mm, no discoloration of the solder joint, process control, and operation in a nitrogen environment.

[0042] The packaging area structure 30 also includes inner pins 32 and outer pins 33 arranged corresponding to the number of chips. The packaging area structure 30 also includes inner pin locking holes 321 arranged inside and outside corresponding to the inner pins. The inner pin locking holes 321 enable the inner pins 30 and the plastic packaging material to be reliably combined. In specific implementation, the packaging area structure 30 is provided with 4 pairs of inner pins 32, outer pins 33, a glue inlet 34, and a plurality of stabilizing reinforcing ribs 35.

[0043] A frame positioning hole 21 is also provided on the side of each group of packaging units 20, a flow channel groove 22 is also provided in the area between the lengthwise intervals of each group of packaging units 20, and a PIN1 identification hole 23 with a semi-circular corner is provided at the lower position of the lower packaging unit of each column of packaging units 20.

[0044] In a specific embodiment, the size specification of the lead frame is 215.46mm×45.7mm, the length tolerance is 215.46mm±0.102mm, the width tolerance is 45.7mm±0.051mm, the heat sink thickness is required to be 1-1.25mm (adjustable according to needs), the pin thickness of the base island is 0.203mm (adjustable according to needs), and the structural surface design of the lead frame is 2 rows, 14 columns in a single row, with a total of 28 packaging units 20.

[0045] Corresponding to the packaging structure of the lead frame in the specific embodiment, each packaging unit 20 includes 4 chips, namely U1, U2, U3, and U4. Figure 6 32 is the inner pin, 1 is the connection line from U3&U4 to the second solder point, that is, the input line, 2 is the BSOB line from U1&U2 to U3&U4, and 3 is the connection line from U3&U4 to the second solder point, that is, the output line; the final packaging structure (see Figure 7-Figure 9) has an appearance size of 15.30mm×5.5mm×4.25mm, the lower mold of the package body adds a demoulding ejector pin φ1mm×2, the upper mold adds 2 ejector pins, the pin1 ejector pin hole is φ1mm, the ejector pin hole is φ1.5mm, and the package body heat sink size is 13.6×3.8mm; the number of pins is 4, the pin spacing e is 5.50mm, and the welding length L1 is 3.05mm. The product maintains the original colloid size type and meets the plastic packaging characteristics.

[0046] The chip packaging method of the packaging mechanism comprises the following steps:

[0047] S1, dicing process, thinning the wafer and then dicing it to form corresponding chips;

[0048] U3 and U4 are MOS chips, and the incoming materials are silver-backed chips with a thickness of 110μm, without thinning. U1 and U2 are chips that do not need to be thinned, and the materials are silver-backed chips with a thickness of 110μm, without thinning. Then, a DISCO dicing machine is used for dicing, and the dicing feed speed is controlled at ≤15mm / s. According to different products and scribe widths, a suitable dicing knife is selected, and it is cleaned and dried in time. Since most wafers are back-gold / back-silver, the wafer material is different from ordinary silicon material, and cracks are prone to occur during dicing. The hazards of cracks can cause reliability risks or functional failures of the product. Solution 1 is to use a double-head dicing machine and double-knife dicing. The first knife cuts 30% of the thickness setting and grooves, and the second knife cuts 70% of the thickness setting to prevent cracks and back collapse. Solution 2 is to select a dicing knife that matches the product, and adjust the parameters such as feed speed and spindle speed through DOE verification, and select optimized parameters for dicing to prevent cracks and back collapse.

[0049] S2, core mounting process, by which the chip is placed at the corresponding position on the upper surface of the heat sink, and glue is applied to complete the chip position curing;

[0050] Adopting full sintering silver process, the equipment adopts core loading machine AD8312plus, core loading oven adopts M-Fine oven, completes three chip loading, one baking solution (multiple baking may cause volatile residues on the chip surface, resulting in abnormal wire bonding), chip thickness 110μm, core loading adopts multi-pin structure (three-step top) to prevent chip top cracking, suction nozzle adopts R3-713 and RT-0.6*4.36, and the plane pinhole structure is designed to effectively avoid chip crack problems, dispensing head diameter 0.4mm, EJ up level650μm, bond force100g, pick force 100g, pick force 100ms, glue pattern drawing......, the chip picking method adopts synchronous picking method, reduces the impact of chip and top pin on chip, reduces cracks, the core glue adopts sintered silver glue, optional models are CTR2700R7S, TS9853, meet the heat dissipation power consumption> 160W / mk, sintered silver sintering has pressure sintering and pressureless sintering, this scheme adopts pressureless sintering, baking conditions: nitrogen-filled oven, according to product requirements, three-stage baking (200℃) or five-stage baking (250℃) can be adopted; baking curve is attached Fig.10 , 11 , monitor the glue climbing height during the operation (do not contaminate the chip surface), control chip cracks and voids within a single ≤3%, overall ≤5%, BLT within 40μm±10, Tilt≤20μm;

[0051] S3, pressure welding and dispensing process, connect the chip with the corresponding inner pins, when the chips need to be connected, connect them through gold wire;

[0052] Pressure welding process: gold wire process (low temperature), the second welding point is located inside the base island, the fixture is designed with a cylinder transmission structure, through software programming and hardware control, the solenoid valve controls the movement of the cylinder, which can meet the transmission in the three directions of X\Y\Z. Through positioning adjustment, the gap between the pad and the pressure plate is ≥0.3mm, which meets the mechanical strength of the fixture and meets the requirements of supporting the wire bonding of the two welding points. Due to the structural design of the dynamic fixture of the two welding points, the conduction temperature of the two welding points is low, the heat conduction is slow, and a longer residence time in the welding area is set. The UPH of the equipment is low, which meets the minimum requirements of wire bonding during the temperature conduction process;

[0053] Press welding equipment model: KNS Iconn plus, the product processes 4 types of chips, preheating temperature 200℃, welding temperature 200℃, U1&U2 to inner pin wire bonding, U3&U4 to inner pin wire bonding, Top: 10mil, one solder joint parameter setting parameter setting Loop Type is forward, EFO fire mode: Ball Size, EFO Gap: 25mils, Tail Extension: 12mils, EFO Fire Control: Before, seg-1 mode: Force, Time: 3ms, Force: 150g, seg-2 Mode: Scrub, Force: 15g, USG Current: 55mAmps, Scrub Frequency: 220Hz, Seg-3 Mode: Force, Force: 16g, Time: 15ms, USG Current: 95mAmps; two solder joint parameters: Seg-1 Mode: Scrub, USGCurrent: 65mAmps, Force: 110g, XY_Distance-12.0, Scrub Amplitude 3.5, ScrubFrequency: 260Hz, Scrub Phase: Circular, seg-2Mode: Scrub, USG Current: 95mAmps, Force: 95g, XY_Distance 3.0, Scrub Amplitude 3.5, Scrub Frequency: 260Hz, ScrubPhase: Circular;

[0054] U1&U2 to U3&U4 connection, U3&U4 connection side Loop type: SSB Bond Selector: SSB Bond1, FabSize: 2.60mils, EFO Gap: 25mils, Tail Extension: 12mils, seg-1mode: Force, Time: 5ms, :150g, seg-2Mode: Scrub, Force: 15g, USG Current: 55mAmps, Scrub Frequency: 220Hz, Seg-3Mode: Force, Force: 16g, Time: 15ms, USG Current: 85mAmps; U1&U2 side, Seg-3 Mode: Force, USG Current: 0mAmps, Force: 65g, XY_Distance-5.0, seg-4Mode: Scrub, USG Current: 60mAmps, Force: 60g, XY_Distance

[0055] 2.0, Scrub Amplitude 3.0, Scrub Frequency: 220Hz, Scrub Phase: Circular, the product welding wire push and pull force meets the process standards;

[0056] Silicone rubber dispensing: material model GDA-3130, processing equipment AD8312plus, viscosity 140000mps, high viscosity, long waiting time for dispensing, dispensing head diameter 0.4mm, dispensing speed 5mm / s, glue coverage area 90%, glue thickness 400μm-900μm, glue pattern: "—", dispensing order, dispensing glue from the middle of the chip position to the left and right in turn, and the middle position is completed. Silicone rubber curing uses M-Fine oven, baking temperature 150℃, baking time 4h, dispensing thickness chip thickness is thicker in the middle and thinner on both sides;

[0057] S4, a plastic encapsulation process, plastic encapsulating the base island of each package unit on the lead frame;

[0058] First plastic sealing: TOWA vacuum system, vacuum mold (non-toothed), equipped with loading and unloading conversion parts, the product application is signal processing, the plastic sealing material must meet the lower DC (4.0MHz), DF (0.01MHz), plastic sealing material selection: EME-G700HF, Φ14mm×6.5g, plastic sealing process parameters: curing time 150s, injection time 10s, preheating time 3s, mold temperature 175℃, mold closing pressure 75T, injection pressure 1.8T, punching rate ≤15%; process monitoring stratification and plastic sealing body voids, monitoring heat sink overflow, after completion, the product maturation conversion rate is about 85%.

[0059] Post-curing: Use M-Fine oven, baking time 10.5h, heating and cooling time 1h each, constant temperature baking 8.5h, constant temperature 175℃, product out-of-box temperature ≤80℃;

[0060] S5, tinning process, tinning the lead frame of the package through an automatic tinning line;

[0061] First, the overflow is removed by hot boiling. The equipment is an automatic softening line, the temperature is 80℃, the pre-immersion is 90 minutes, the tap water is washed, the deionized water is washed, and the overflow is removed by high-temperature ion drying;

[0062] Tinning adopts automatic tinning line to tin the semi-finished multi-row matrix HSOF4L lead frame. By improving the shielding plate structure of the electroplating tank and realizing the automatic operation of the shielding plate, the shielding plate is used to disperse the power lines in the high current area, thereby reducing the current intensity in the high current area, so as to improve the uniformity of the coating thickness. The coating thickness of the product is controlled at 11.43±3.81μm.

[0063] After tinning, the product is returned and baked and dehumidified, with an annealing temperature of 150°C and a baking time of 1h, and a dehumidification baking temperature of 125°C and a baking time of 4h;

[0064] S6, printing process, printing the trademark on the surface of the plastic package;

[0065] The printing equipment model is HTM-3025B, using Ted laser, marking parameters: power (W) 87, frequency 76KHZ, speed 700 / 420mm / s, using fixture fixation, full-automatic laser printing, continuous feeding positioning printing method, trademark printing on the surface of the plastic package, the product is a series with exposed heat sink, which meets the requirements of product positive printing.

[0066] S7, cutting and separating the ribs, cutting off the middle rib connecting rod connected to the lead frame to obtain an independent packaging structure;

[0067] A dedicated rib cutting system and mold are used. The supplier is GMM. The center rib connecting rod connected to the frame is cut. The gap between the rib cutting tool and the plastic package body is greater than 0.05mm to ensure that the plastic package body is not cut. At the same time, the plastic package residue on the surface of the mold is cleaned to reduce the damage of the colloid. The product pins are not formed (straight legs) and are completed using a separation cutting mold.

[0068] Its working principle is as follows: a laser welding process is used on the lead frame to assemble the heat sink on the base island area of ​​the lead frame. Compared with the traditional lead frame manufacturing method, this technology has a smaller heat-affected zone, smaller thermal deformation, better welding quality, and no special environmental requirements. At the same time, for the high reliability and high heat dissipation characteristics of the product, the lead frame adopts a thick heat sink and thin pin connection method. The material uses high thermal conductivity material KFC. The heat sink is exposed to ensure good heat dissipation performance. High thermal conductivity fully sintered silver is used between the chip and the lead frame to meet the heat dissipation capacity ≥160W / mk, which solves the problems of good electrical conductivity and high heat dissipation. It enables the lead frame to have high heat dissipation performance, so that it can adapt to high reliability products and ensure reliable operation of the product.

[0069] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0070] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A lead frame structure of a special-shaped high heat sink, characterized in that: It includes a frame body, which is a rectangular structure. A plurality of packaging units are arranged in an array within the surface area of ​​the frame body. Each packaging unit includes a packaging area structure and a heat sink. The heat sink is a thick sheet body. The packaging area structure is provided with thin pins at both ends of the heat sink in the length direction. The inner convex part of the thin pin is connected to the upper surface of the two ends of the heat sink in the length direction by laser welding. The chip is placed on the upper surface of the heat sink.

2. The lead frame structure of a special-shaped high heat sink according to claim 1, characterized in that: The connection between the heat sink and the thin pin is a π-shaped welding structure, and the welding points are all located inside the surface area of ​​the heat sink.

3. The lead frame structure of a special-shaped high heat sink according to claim 1, characterized in that: The thickness of the heat sink is 1-1.25 mm, the main body material of the heat sink is KFC, and the surface of the heat sink is fully silver-plated.

4. The lead frame structure of a special-shaped high heat sink according to claim 1, characterized in that: The upper surface of the heat sink is provided with heat sink front locking grooves on both sides in the width direction.

5. The lead frame structure of a special-shaped high heat sink according to claim 1, characterized in that: A plurality of Dimple are also arranged on the upper surface of the heat sink, and the positions of the Dimple can be flexibly adjusted according to product requirements.

6. The lead frame structure of a special-shaped high heat sink according to claim 1, characterized in that: The back side of the heat sink is provided with a back side locking step with a concave edge.

7. The lead frame structure of a special-shaped high heat sink according to claim 1, characterized in that: The packaging area mechanism also includes inner pins and outer pins arranged corresponding to the number of chips, and the packaging area mechanism also includes inner pin locking holes arranged inside and outside corresponding to the inner pins.

8. A chip packaging method using a lead frame structure with a special-shaped high heat sink as claimed in any one of claims 1 to 7, characterized in that: It includes the following steps: S1, dicing process, thinning the wafer and then dicing it to form corresponding chips; S2, core mounting process, by which the chip is placed at the corresponding position on the upper surface of the heat sink, and glue is applied to complete the chip position curing; S3, pressure welding and dispensing process, connect the chip with the corresponding inner pins, when the chips need to be connected, connect them through gold wire; S4, a plastic encapsulation process, plastic encapsulating the base island of each package unit on the lead frame; S5, tinning process, tinning the lead frame of the package through an automatic tinning line; S6, printing process, printing the trademark on the surface of the plastic package; S7, cutting and separating the ribs, cutting off the middle rib connecting rod connected to the lead frame to obtain an independent packaging structure.

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