A method of injection molding a flat frame for semiconductor packaging

Abstract

The application discloses a kind of injection molding methods of semiconductor packaging flat plate frame, it is related to semiconductor packaging technical field.The method includes: loading in fully enclosed cabin;Subsequently, pre-evacuation mold clamping and injection molding are carried out: upper and lower mould is closed to preset distance but is not locked, injection rod plug is pushed to preset height to advance to discharge part cavity gas;Then, main mold clamping and multi-section injection molding are carried out: after mold is completely locked, injection rod plug is carried out fine injection molding according to multi-section program;Finally, solidification and mold opening are carried out.The application is synergized by fully enclosed environment, pre-evacuation and multi-section injection molding, effectively solve the defects problems such as plastic package body blowhole, sand eye caused by large mold temperature difference, poor gas discharge and extensive injection molding process, can significantly reduce the blowhole proportion of SOP8 flat plate frame plastic package product by 50%-80%, improve product yield and reliability.

Description

Technical Field

[0001] This invention relates to the field of semiconductor packaging technology, and in particular to an injection molding method for a flat plate frame for semiconductor packaging. Background Technology

[0002] In the molding process of semiconductor packaging and testing companies, molding involves using epoxy molding compound (EMC) to encapsulate and protect components such as wafers and lead frames under high temperature and pressure, ultimately forming a shell. Currently, SOP packaging mostly uses multi-piece molding (MGP) equipment. In this process, the mold chamber is usually in an open or semi-open environment during molding, and after mold closing, molding is completed through three-stage injection molding with simultaneous venting.

[0003] However, the above-mentioned technologies have obvious shortcomings:

[0004] 1. Uneven mold temperature: The open molding environment causes the air conditioning airflow in the production site to directly impact the mold surface, resulting in a large temperature difference between the front and back areas of the mold. This affects the uniformity of EMC flowability and can easily lead to incomplete filling or internal stress.

[0005] 2. Gas Residue Formation Defects: Because the wafer, leads, and other structures are concentrated on one side of the frame, there is a significant difference in flow resistance between the two sides of the cavity after mold closing. During injection molding, the side with faster EMC flow rate is prone to trapping gas from the slower flow side, forming encapsulation defects such as pinholes and bubbles, which seriously affect product yield and reliability.

[0006] 3. Poor process adaptability: The traditional three-stage injection molding (slow-fast-slow / holding pressure) mode has limited optimization space for products with complex designs such as die bonding and pressure welding, and with many chips and large volume (such as highly integrated devices such as SOP8). It is difficult to effectively reduce the porosity by finely adjusting the injection molding parameters.

[0007] Therefore, there is an urgent need for a molding encapsulation method that can improve the uniformity of the mold temperature field, effectively expel cavity gas, and achieve precise injection molding control in order to improve the quality of semiconductor flat panel frame packaging products. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the purpose of the present invention is to provide an injection molding method for a flat plate frame for semiconductor packaging, so as to solve the problems of uneven mold temperature, gas residue formation defects and poor process adaptability.

[0009] An injection molding method for a flat plate frame for semiconductor packaging, the method being performed in a molding press having an independent sealed chamber, includes the following steps:

[0010] S1. Preparation and loading: Preheat the flat plate frame and EMC cake; close the front door of the molding press, and the loading mechanism carries the preheated flat plate frame and EMC cake into the sealed chamber through the rear door; place the flat plate frame into the lower mold cavity and put the EMC cake into the injection molding tube; after completion, the loading mechanism exits and the rear door is closed, forming a fully enclosed working environment.

[0011] S2, Pre-venting mold closing and injection molding: Control the upper mold and lower mold to close to a preset distance D1. At this time, the mold is not completely locked. Then, drive the injection rod to push up to a preset height H1. During this process, EMC is not injected into the cavity, and some gas in the cavity is discharged through the mold gap.

[0012] S3. Main mold closing and multi-stage injection: Control the upper mold and lower mold to completely close and lock; then, start the multi-stage injection program, and the injection rod advances according to the preset multi-stage stroke curve. Each stroke corresponds to a different injection speed and pressure, injecting molten EMC into the cavity;

[0013] S4. Curing and Mold Opening: Maintain temperature and pressure to cure EMC, then open the mold and remove the product.

[0014] The beneficial effects of this invention are:

[0015] 1. Fully enclosed chamber design: This fundamentally eliminates the interference of ambient airflow on mold temperature, ensuring the uniformity of the mold temperature field during the molding process and creating a prerequisite for the smooth flow of EMC.

[0016] 2. Innovative pre-venting step: By utilizing the incomplete mold gap and the pre-action of the injection plug before the mold is fully closed and locked, a portion of the air in the cavity is actively vented, significantly reducing the risk of pinholes and bubbles formed due to EMC back-encapsulation of gas in the subsequent main injection stage.

[0017] 3. Multi-stage precision injection molding: The traditional three-stage injection molding is expanded to multi-stage (at least four-stage) injection molding, which allows for the use of optimal injection speed and pressure at different filling stages according to the structural characteristics of the frame cavity, so as to achieve smooth and orderly filling and further reduce the probability of porosity.

[0018] 4. Significant synergistic effect: The above three improvement measures work together to reduce the porosity of flat frame plastic-encapsulated products by 50% to 80%, which has been verified in practice, greatly improving the packaging quality, reliability and production yield of the products. Attached Figure Description

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0020] Figure 1 This is a flowchart of the injection molding method in this embodiment. Detailed Implementation

[0021] This invention provides an injection molding method for a flat plate frame for semiconductor packaging. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0022] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0023] Please see Figure 1 :

[0024] Figure 1 This is a flowchart of the injection molding method according to an embodiment of the present invention. The left diagram is the overall process flow diagram, showing the complete process from preparation and material loading to curing and mold opening. The right diagram is a detailed process flow diagram of the "mold closing" and "injection molding" steps in the left diagram, further showing the detailed steps of the mold closing and injection molding stages. The arrows in the diagram indicate the sequential execution relationship between the steps.

[0025] This embodiment discloses an injection molding method for a semiconductor packaging flat panel frame, which is particularly suitable for SOP8 flat panel frames. The specific steps are as follows:

[0026] S1. Preparation: Preheat the flat plate frame (with chips attached and wire bonding completed) and the EMC pie. The preheating temperature is set according to the characteristics of the selected EMC material, usually between 80℃ and 95℃.

[0027] S11. Feeding: The operator or automated equipment confirms that the front door of the molding press is closed and locked. Then, the feeding mechanism (such as a robotic arm) enters the independent, sealed chamber of the molding press through the rear door. The preheated flat frame is precisely placed on the cavity positioning device of the lower mold, and the EMC cake is simultaneously fed into the injection molding cylinder. After completion, the feeding mechanism exits, and the rear door closes automatically. At this point, the entire molding operation space forms a fully enclosed chamber isolated from the external environment, effectively preventing uneven cooling of the mold by external airflow such as air conditioning.

[0028] S2, Pre-exhaust stage:

[0029] S21, Mold Closure 1: The upper mold moves downward and closes with the lower mold at a preset distance D1, D1=1.0mm. This distance ensures that the mold is not completely clamped and locked, and the cavity communicates with the interior of the fully enclosed chamber through this gap.

[0030] S22, Injection 1: The injection drive mechanism moves, pushing the injection plunger upwards by a preset height H1, where H1 = 10% of the total stroke (approximately corresponding to the discharge of 22% of the original cavity gas). (This height is determined through calculation and experimentation to ensure that the EMC melts in the barrel but has not yet been pushed into the mold runner and cavity). This action is equivalent to an "air push," the purpose of which is to use the movement of the plunger to pre-expel a portion of the air in the cavity and runner system through the aforementioned mold gap (D1). This step is a crucial pilot venting step.

[0031] S3, Main Injection Molding Stage:

[0032] S31, Mold Closure 2: After pre-venting, the upper mold continues to descend, completely closing with the lower mold and applying sufficient clamping force to lock it in place.

[0033] S31, Injection 2: The injection rod plunger advances according to a preset multi-segment injection program. Taking a four-segment program as an example:

[0034] Section 1: Low-speed filling. Injection begins at a low speed V1 and pressure P1 to ensure the EMC enters the cavity smoothly, avoiding impact on the chip and leads. V1 = 10 mm / s, P1 = 3 MPa, filling to approximately 15% of the cavity volume.

[0035] Section 2: Medium-speed stabilization. After the EMC flows through critical areas (such as chip edges), the flow rate is switched to medium speed V2 and pressure P2 for stable filling. V2 = 25 mm / s, P2 = 5 MPa, filling to approximately 60% of the cavity volume.

[0036] Section 3: High-speed filling. When most of the cavity is filled and the flow resistance is relatively stable, a higher speed (V3) and pressure (P3) are used for rapid filling to shorten the overall injection molding time. V3 = 50 mm / s, P3 = 8 MPa, filling to approximately 95% of the cavity volume.

[0037] Section 4: Low-speed holding pressure. Towards the end of the filling process, reduce the speed to a low V4 and maintain pressure P4 for a period to compensate for EMC curing shrinkage, ensuring uniform molded body density and reducing pinholes. Multiple parameters can be optimized through simulation and experimentation based on the specific product structure. Specifically, V4 = 8 mm / s, P4 = 12 MPa, and holding pressure for 10 seconds.

[0038] S4. Curing and Mold Opening: After injection molding, maintain a curing temperature of 170℃-185℃ and a pressure of 12MPa for 90 seconds to allow the EMC to fully cross-link and cure. After curing, open the mold and remove the molded SOP8 product by the ejection mechanism or a robot.

[0039] Sampling ultrasonic scanning (SAM) and visual inspection were performed on 2,000 products produced using the above process. The results showed that the internal porosity defect rate was 1.2% and the external pinhole defect rate was 0.6%, indicating a significant improvement in product quality.

[0040] Therefore, this method is particularly suitable for flat frame products like SOP8 that have high requirements for airtightness and appearance. It can systematically solve the pain points of traditional processes and significantly improve product quality.

[0041] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of the present invention.

Claims

1. An injection molding method for a flat plate frame for semiconductor packaging, characterized in that, This method is performed in a plastic sealing press with an independent, sealed compartment and includes the following steps: S1. Preparation and loading: Preheat the flat plate frame and EMC cake; close the front door of the molding press, and the loading mechanism carries the preheated flat plate frame and EMC cake into the sealed chamber through the rear door; place the flat plate frame into the lower mold cavity and put the EMC cake into the injection molding tube; after completion, the loading mechanism exits and the rear door is closed, forming a fully enclosed working environment. S2, Pre-venting mold closing and injection molding: Control the upper mold and lower mold to close to a preset distance D1. At this time, the mold is not completely locked. Then, drive the injection rod to push up to a preset height H1. During this process, EMC is not injected into the cavity, and some gas in the cavity is discharged through the mold gap. S3. Main mold closing and multi-stage injection: Control the upper mold and lower mold to completely close and lock; then, start the multi-stage injection program, and the injection rod advances according to the preset multi-stage stroke curve. Each stroke corresponds to a different injection speed and pressure, injecting molten EMC into the cavity; S4. Curing and Mold Opening: Maintain temperature and pressure to cure EMC, then open the mold and remove the product.

2. The injection molding method for a semiconductor packaging plate frame according to claim 1, characterized in that, The preset distance D1 ranges from 0.5mm to 2mm.

3. The injection molding method for a semiconductor packaging plate frame according to claim 1, characterized in that, The preset height H1 is set to ensure that EMC does not enter the cavity.

4. The injection molding method for a semiconductor packaging plate frame according to claim 1, characterized in that, The multi-stage injection molding process includes at least four injection strokes.

5. The injection molding method for a semiconductor packaging plate frame according to claim 4, characterized in that, The at least four injection strokes are, in sequence, a first low-speed filling segment, a second medium-speed stabilizing segment, a third high-speed filling segment, and a fourth low-speed holding segment.

6. The injection molding method for a semiconductor packaging plate frame according to claim 1, characterized in that, In step S1, the fully enclosed working environment ensures that the surface temperature of the mold is uniform and the temperature difference is controlled within ±3℃.

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