Silver colloid diffusion preventing agent for lead frame and technological process of silver colloid diffusion preventing agent

Abstract

The invention relates to a silver colloid diffusion preventing agent for a lead frame and a technological process of the silver colloid diffusion preventing agent, and relates to the technical field of semiconductor lead frame packaging. 2%-2.5% of a silane coupling agent KHH560; 1.5%-2% of a waterborne polyurethane emulsion; 1.5%-2% of 1, 2-propylene glycol; 0.4%-0.8% of choline chloride; 0.2% to 0.4% of isophorone diisocyanate; and the balance of water. Through the synergistic film forming effect of the hydroxyl silicone oil and the silane coupling agent, a compact protection layer is formed on the surface of the lead frame, silver ion migration can be inhibited, pollution to a bonding pad of the lead frame is effectively reduced, and the stability and the service life of an electronic device are ensured.

Description

Technical Field

[0001] This application relates to the technical field of semiconductor leadframe packaging, and in particular to an anti-silver paste dispersant for leadframes and its process flow. Background Technology

[0002] Conductive silver paste is a functional adhesive that combines adhesion and conductivity. It is primarily composed of a base resin (such as epoxy resin), conductive filler (silver powder), and additives such as curing agents and dispersants. In the field of electronic packaging, it achieves interconnection between discrete devices and lead frames through the pathways formed by the conductive filler, and is widely used for bonding lead frame chips. Compared to traditional Sn-Pb solder, conductive silver paste has advantages such as simple processing and low curing temperature, effectively avoiding problems such as component deformation, weak adhesion, and performance degradation caused by soldering.

[0003] During the encapsulation process, if the bonding surface (such as a gold-plated, silver-plated, copper-plated, or palladium-plated substrate) has excessive surface roughness or is covered by contaminants such as protective agents or oil, it can cause the epoxy resin or other components in the conductive silver paste to seep out (i.e., silver paste diffusion). This phenomenon may cause the diffused conductive particles to become ionized and initiate electrochemical migration, leading to a short circuit.

[0004] Silver paste diffusion during chip bonding can lead to unreliable bonding, and the ionization of conductive particles may even cause electrochemical migration, resulting in short circuits. Therefore, it is urgent to improve the formulation or process of conductive adhesives to solve the diffusion problem and improve packaging reliability. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an anti-silver paste diffusion agent for lead frames and its process flow. It solves the technical problem that silver paste diffusion occurs during the chip bonding process, which leads to unreliable bonding between the chip and the lead frame, and even the ionization of conductive particles may cause electrochemical migration, resulting in short circuits.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A lead frame anti-silver paste dispersant comprises the following components by mass percentage: 1.2%-1.6% hydroxyl silicone oil; 2%-2.5% silane coupling agent KHH560; 1.5%-2% waterborne polyurethane emulsion; 1.5%-2% 1,2-propanediol; 0.4%-0.8% choline chloride; 0.2%-0.4% isophorone diisocyanate; and the balance is water.

[0008] Furthermore, the hydroxyl silicone oil is dimethyl hydroxyl silicone oil or terminal hydroxyl silicone oil.

[0009] Furthermore, the solid content of the waterborne polyurethane emulsion is 30%-50%.

[0010] A process for preventing silver paste diffusion in lead frames includes the following steps:

[0011] S1 involves pre-cleaning, washing, and alkaline roughening of the lead frame;

[0012] S2 involves immersing the lead frame treated in step S1 in the anti-silver paste diffusion agent described in claim 1, controlling the solution temperature at 25-30°C, the treatment time at 30-50 seconds, the pH value at 6-7, and the concentration at 6%-10%.

[0013] S3 involves washing the lead frame processed in step S2 with water, then performing copper protection treatment, and finally drying.

[0014] Furthermore, the pre-cleaning process involves mechanical cleaning with a soft-bristled brush for 8-12 seconds.

[0015] Furthermore, the alkaline roughening treatment uses an alkaline solution with a concentration of 3%-6%, a temperature of 20-35℃, and a time of 10-20 seconds.

[0016] Furthermore, the copper protection treatment uses Atotech EBO series chemicals at a temperature of 30-45℃ for 30-60 seconds.

[0017] Furthermore, the drying process includes roller water absorption, cold air drying for 10-15 seconds, hot air drying at 50-80°C for 40-60 seconds, and cold air cooling for 10-15 seconds.

[0018] As described above, the anti-silver paste diffusion agent is used in semiconductor lead frame packaging processes to form a dense protective layer on both the SO side (soldering side) and the CO side (chip side) to suppress the diffusion of silver paste during the natural curing process.

[0019] A semiconductor packaging structure includes a lead frame processed by any of the above processes, and a chip bonded to the lead frame by conductive silver paste, wherein a dense protective layer is formed on the surface of the lead frame.

[0020] In summary, this application includes at least one of the following beneficial technical effects of an anti-silver paste dispersant for lead frames and its processing flow:

[0021] 1. Through the synergistic film-forming effect of hydroxyl silicone oil and silane coupling agent, a dense protective layer is formed on the surface of the lead frame, which can prevent the diffusion of silver paste and reduce pad contamination and electrochemical migration;

[0022] 2. It can handle lead frames of different materials such as gold-plated, silver-plated, and copper-plated, and is compatible with Atotech EBO copper protection solution, which can be implemented without modifying existing equipment;

[0023] 3. The drying process adopts staged temperature control, cold air → hot air → cold air, which reduces energy consumption compared with traditional processes and reduces the amount of solution carried out. Attached Figure Description

[0024] Figure 1 This application mainly provides a comparative test diagram of the presence and absence of anti-silver paste diffusion treatment;

[0025] Figure 2 This is a schematic diagram of the comparison test between alkaline roughening and non-alkaline roughening, which is the main feature of this application;

[0026] Figure 3 This is a schematic diagram showing the comparison test of different concentrations of anti-silver paste dispersant and different treatment times, which is the main feature of this application.

[0027] Figure 4 This is a schematic diagram showing the comparison test of different brands of silver paste provided in this application. Detailed Implementation

[0028] To facilitate a clear understanding of the technical means, creative features, objectives, and effects of this invention, the invention will be further described below in conjunction with specific embodiments.

[0029] The following is in conjunction with the appendix Figure 1-4 This application will be described in further detail.

[0030] This application discloses an anti-silver paste dispersant for lead frames and its process flow.

[0031] The components of the anti-silver paste dispersant are shown in Table 1.

[0032]

[0033] Table 1. Components of Anti-Silver Coating Dispersant

[0034] The main uses of anti-silver paste dispersant include:

[0035] Reduce conductive silver paste diffusion: Anti-silver paste diffusion agent inhibits silver paste diffusion by forming a dense protective layer on the lead frame or other substrate surface, ensuring that the soldering area is not affected.

[0036] Improved solderability: After the silver paste is applied to the soldering position, it ensures good solderability and avoids soldering failure caused by the diffusion material covering the solder pad.

[0037] Preventing electrical short circuits: Reduces the migration of silver powder particles in conductive silver paste, preventing electrochemical migration from causing short circuits.

[0038] Process parameter control: working temperature 25-30℃, processing time 30-50S, pH value 6-7, concentration 6-10%.

[0039] The decrease in the concentration of the anti-silver paste dispersant working solution is mainly due to carry-over consumption. During use, the anti-silver paste dispersant should be added accordingly based on the amount of carry-over consumption. The tank should be changed periodically according to the production area; a change frequency of 3-6 days is recommended.

[0040] The processes preceding this procedure must be kept neutral, as both acidity and alkalinity will affect the performance of the anti-silver paste dispersant.

[0041] The different process flows before dispensing testing are as follows:

[0042] Process A (Full Process): Feeding → Pre-cleaning → Water washing → Alkaline roughening → Water washing → Anti-silver paste diffusion treatment → Water washing → Copper protection → Water washing → Drying treatment → Discharge → Dispensing test

[0043] Process B (without anti-silver paste diffusion treatment): Feeding → Pre-cleaning → Water washing → Alkaline roughening → Copper protection → Water washing → Drying → Discharge → Dispensing test

[0044] Process C (non-alkaline roughening): Feeding → Pre-cleaning → Water washing → Anti-silver paste diffusion treatment → Water washing → Copper protection → Water washing → Drying treatment → Discharge → Dispensing test

[0045] Process description:

[0046] Pre-cleaning: Mechanical cleaning with a soft-bristled brush (nylon / PVA material) for 8-12 seconds to reduce the risk of scratching delicate lines;

[0047] Water washing: counter-current water washing, temperature 20-35℃, processing time 10-15s;

[0048] Alkaline roughening: Temperature 20-35℃, treatment time 10-20s, maintain the concentration of alkaline roughening solution in the range of 3%-6%;

[0049] Anti-silver paste diffusion treatment: The solution is the anti-silver paste diffusion agent of this application, the temperature is 25-30℃, the treatment time is 30-45s, the concentration of the anti-silver paste diffusion agent is 6%-10%, and the pH value of the solution is maintained at 6-7.

[0050] Copper protection: The solution is from the Atotech EBO series, the temperature is 30-45℃, and the treatment time is 30-60 seconds.

[0051] Drying: roller absorbs water → cold air blows dry for 10-15 seconds → hot air dries (50-80℃, 40-60 seconds) → cold air cools for 10-15 seconds;

[0052] Silver glue spot test: Warm the refrigerated silver glue to room temperature, squeeze a drop from the needle tip onto the plastic sheet, stir with the drill bit for 30 seconds, and then drop it onto the test plate.

[0053] like Figure 1 Comparison of treatments with and without silver paste diffusion prevention.

[0054] Process A (anti-silver paste diffusion treatment: anti-silver paste diffusion agent concentration 8%, treatment time 40s) and Process B (no anti-silver paste diffusion treatment) were compared to illustrate the effect of anti-silver paste diffusion treatment on silver paste diffusion under the same conditions. (Silver paste used: LOCTITE ABLESTIK 8290)

[0055] Conclusion: For samples with full-process treatment, no silver paste diffusion was observed in multiple measurements at different placement times when silver paste was applied to the CO and SO surfaces. For samples without anti-silver paste diffusion treatment, significant silver paste diffusion was observed in multiple measurements at different placement times when silver paste was applied to the CO and SO surfaces.

[0056] like Figure 2 Comparison of alkaline roughening with and without.

[0057] Process A (anti-silver paste diffusion treatment: anti-silver paste diffusion agent concentration 8%, treatment time 40s) includes alkaline roughening treatment, while Process C (anti-silver paste diffusion treatment: anti-silver paste diffusion agent concentration 8%, treatment time 40s) does not include alkaline roughening treatment. The effect of alkaline roughening on silver paste diffusion is compared under the same conditions. (Silver paste used: LOCTITE ABLESTIK8290)

[0058] Conclusion: In the spot-coating tests of multiple samples after the entire process, no silver paste diffusion was observed in multiple measurements. In the spot-coating tests of multiple samples without alkaline roughening treatment, slight silver paste diffusion was observed in multiple measurements, with a maximum diffusion range of 0.054 mm.

[0059] like Figure 3 Comparative tests of different concentrations of anti-silver paste dispersant and different treatment times

[0060] Procedure A involves adjusting the concentration and treatment time of the anti-silver paste dispersant to compare the effect of concentration on silver paste diffusion under the same conditions. (The silver paste used is: LOCTITE ABLESTIK 8290)

[0061] Conclusion: When silver paste was applied to multiple sample points within the concentration range and processing time of the entire process, no silver paste diffusion was observed in the multi-point measurements.

[0062] like Figure 4 Comparison of different brands of silver paste

[0063] Process A (anti-silver paste diffusion treatment: anti-silver paste diffusion agent concentration is 8%, treatment time is 40s) was followed by dotting of different brands of silver paste. The treatment effect of the anti-silver paste diffusion agent on different silver pastes (LOCTITE ABLESTIK 8290, LOCTITE ABLESTIK 84-3J, HeraGlue PD-030, SE-4470) was compared under the same conditions.

[0064] Conclusion: Multiple samples processed throughout the entire process were tested with silver paste from different brands, and no silver paste diffusion was observed in any of the multi-point measurements.

[0065] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A silver paste dispersant for lead frames, characterized in that, It includes the following components by mass percentage: Hydroxysilicone oil 1.2%-1.6%; Silane coupling agent KHH560 2%-2.5%; Waterborne polyurethane emulsion 1.5%-2%; 1,2-Propanediol 1.5%-2%; Choline chloride 0.4%-0.8%; Isophorone diisocyanate 0.2%-0.4%; The remainder is water.

2. The anti-silver paste dispersant for lead frames according to claim 1, characterized in that, The hydroxyl silicone oil is dimethyl hydroxyl silicone oil or terminal hydroxyl silicone oil.

3. The anti-silver paste dispersant for lead frames according to claim 1, characterized in that, The solid content of the waterborne polyurethane emulsion is 30%-50%.

4. A process for preventing silver paste diffusion in lead frames, characterized in that, Includes the following steps: S1 involves pre-cleaning, washing, and alkaline roughening of the lead frame; S2 involves immersing the lead frame treated in step S1 in the anti-silver paste diffusion agent described in claim 1, controlling the solution temperature at 25-30°C, the treatment time at 30-50 seconds, the pH value at 6-7, and the concentration at 6%-10%. S3 involves washing the lead frame processed in step S2 with water, then performing copper protection treatment, and finally drying.

5. The anti-silver paste diffusion treatment process for lead frames according to claim 4, characterized in that, The pre-cleaning process involves mechanical cleaning with a soft brush for 8-12 seconds.

6. The anti-silver paste diffusion treatment process for lead frames according to claim 4, characterized in that, The alkaline roughening treatment uses an alkaline solution with a concentration of 3%-6%, a temperature of 20-35℃, and a time of 10-20 seconds.

7. The anti-silver paste diffusion treatment process for lead frames according to claim 4, characterized in that, The copper protection treatment uses Atotech EBO series chemicals at a temperature of 30-45℃ for 30-60 seconds.

8. The anti-silver paste diffusion treatment process for lead frames according to claim 4, characterized in that, The drying process includes roller water absorption, cold air drying for 10-15 seconds, hot air drying at 50-80℃ for 40-60 seconds, and cold air cooling for 10-15 seconds.

9. A semiconductor packaging structure, characterized in that, The device includes a lead frame processed by any of claims 4-8, and a chip bonded to the lead frame by conductive silver paste, wherein a dense protective layer is formed on the surface of the lead frame.

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