Analysis of air holes and bubbles in the most popu

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Analysis of pores and bubbles in integrated circuit packaging products

Abstract: This paper analyzes the causes of common pores and bubbles in integrated circuit packaging products, and puts forward improvement methods to improve the qualification rate of packaging products

key words: integrated circuit packaging products pore bubble plastic packaging mold

1 introduction

the storage capacity of integrated circuits increases several times every new year, and the plastic packaging shape of chips is becoming smaller. Thin direction. Therefore, the semiconductor packaging industry is becoming increasingly important, putting forward higher requirements for plastic packaging molds. The packaging material is not suitable for wide samples (plastic packaging materials). It is a mixture of epoxy resin as the base water component and various additives. It has only the characteristics of moisture resistance, flame resistance, easy storage, good flow filling, high electrical insulation, low stress, high strength, good reliability and so on. For a long time, it has been used in the surface low-voltage packaging of integrated circuits, semiconductors and passive devices

the packaging process of integrated circuits is shown in Figure 1: ① pressurize the powdered resin, mold it and make it into plastic packaging cake; Before packaging, preheat the cake with high-frequency top heater; ② The cake with fast reaction after preheating is put into the barrel of the mold; ① The chess injection head applies pressure to the cake, and the grease fills the mold cavity through the runner and gate; ④ The injection head continues to maintain pressure, and the resin has sufficient crosslinking and curing reaction in the mold, hardening and molding; ① Open the mold and take out the packaged integrated circuit products

it is very important to measure the quality index of integrated circuit plastic package. This paper analyzes the reasons for the small packaging process and the bubbles on the surface and inside of the plastic package. The bubbles not only reduce the strength of the plastic package, but also greatly reduce the moisture resistance and electrical insulation performance, which will have a great impact on the reliability of the safe use of integrated circuits. Serious cases will lead to the failure of integrated circuit manufacturing, leaving potential safety hazards for the use of electrical appliances

2 analysis of the problem of pores or bubbles in plastic packaging

bubbles or pores on the surface or inside of plastic packaging are quality defects. The problems causing this defect are: ① the plastic sealing material is not well kept, and the absorbed water will generate gas and remain in the sealing products when the plastic is formed at high temperature; ② The design of the mold is unreasonable. When the plastic is filled, all kinds of gases in the mold cannot be quickly and effectively discharged (including the air in the closed cavity, volatile gases generated during the curing of the plastic sealant, captured water vapor and various volatile substances): ③ the lead frame is not fully preheated, which hinders the flow performance of the plastic; ④ The debugging process parameters of the mold are incorrect

in order to ensure that the performance of the plastic packaging material used in the plastic packaging mold will not change, the molded plastic packaging material cake needs to be stored in an environment lower than 5 ℃. Therefore, before formal use, the refrigerated plastic packaging material cake should be placed at room temperature 24h in advance to thaw, commonly known as "waking material", before use. If the temperature return time is not enough, the plastic packaging material is not fully awake, and the temperature is lower than the ambient temperature, the cake will absorb the moisture in the air when it is mixed. When the cake enters the high-temperature cavity of the mold, the absorbed water will quickly evaporate into water vapor at the temperature of 175 ℃, and the volume will expand many times. It is difficult to eliminate it when it is mixed with the plastic packaging material. When the plastic is cured, these gases will be separated out on the surface of the plastic packaging body or form pores and bubbles inside

there are pores and bubbles in the plastic package, which is closely related to the quality of the mold design. The depth and filling angle of the feed port of the mold determine the flow direction of the plastic in the mold and the position of the final fusion mark. As a product requirement, the mold designer hopes that the plastic will be filled in the mold from near to far, and finally the fusion mark will remain near the air groove until it disappears. As for how plastic is filled in the mold cavity, so far, there is no complete theory in the industry to guide designers, but more rely on experience to design. From this point, it is very important for an excellent mold designer to be good at summarizing experience. In order to exhaust all the gas in the mold cavity, the mold must be designed with an exhaust slot. If the packaging conditions permit, exhaust slots should be designed as much as possible to ensure that the gas can be quickly and completely discharged during the plastic filling process. If the exhaust effect is not good, the gas in the mold will produce a "back pressure" effect, and large holes will be generated on the surface of the plastic package, which will seriously affect the quality of the plastic package products. A good exhaust slot can not only discharge all the gas in the mold, but also ensure that there is no excessive overflow in the air slot. The integrated circuit lead strip needs to be preheated before packaging. If the temperature is too low, If the plastic sealant entering the cavity contacts with the cold surface of the strip, it will increase the viscosity, weaken its flow performance, and produce incomplete packaging. Before the normal production of the mold, its state needs to be adjusted to find out the most appropriate production process parameters: (1) preheating temperature. If the preheating temperature of the plastic packaging material is too low, its viscosity will increase, and it is easy to wrap air during flow filling. If the temperature is too high, the plastic packaging material will solidify in advance and cannot continue to flow; ① Injection speed of plastic packaging material. Too fast injection. Before the gas is discharged from the mold cavity, the plastic sealing material reaches near the exhaust slot, which prevents the gas from continuing to be discharged. The gas remaining in the mold cavity is molded together with the plastic. Too slow speed will lead to the curing of the plastic packaging material before it is fully filled, and the filling of the cavity is not allowed: ③ the temperature of the plastic packaging mold. If the mold temperature is too high and exceeds the glass point conversion temperature of the plastic packaging material, the viscosity of the resin will increase, and it has enough elasticity to withstand the pressure of the internal trapped gas under the action of the injection pressure. When the external pressure is cancelled, the internal gas is released and bubbles are formed. Generally, the mold instrument uses epoxy resin, and the temperature is controlled within 175 ± 5 ℃, which can effectively eliminate the influence of mold temperature

3 improvement method

(1) pay attention to the storage and use of plastic packaging materials. When rewarming, the cake should be placed in a closed polyethylene plastic bag with desiccant. Pay attention to avoid exposure to the air to absorb moisture. The cake not used for the time being shall be kept in strict accordance with - 8.4 the declaration of conformity shall include the requirements of the regulations and standards to be observed to prevent failure

(2) attention should be paid to drawing on previous successful experience in mold design. Learn to bypass by analogy, find out the law of experimental flow such as resin rate from the successful cases of past design, and summarize the experience value of gate design. The exhaust slot shall be designed as wide as possible, with more quantity and shorter length, so as to facilitate the rapid discharge of gas. The clearance of the ejector rod should be reasonable, taking into account the exhaust effect

(3) the traditional single cylinder plastic packaging mold has a narrow range of plastic packaging production process, so pay attention to careful debugging. For products with pores and bubbles, analyze the causes, and change a certain parameter day by day until the best production process parameters are called out. In the process of debugging the mold, it should be noted that the actual temperature of the mold will be lower than the temperature shown by the thermocouple meter. You should use the thermometer to measure the temperature of the mold and measure it at multiple points to be aware of it

(4) during the production process of the mold, the resin with excellent flow performance will be everywhere. The residual resin at the exhaust will hinder the discharge of gas. Therefore, the exhaust slot on the parting surface needs to be cleaned frequently, and the overflow on the mold surface should be removed to prevent blocking the exhaust slot. It is necessary to clean and dry the ejector pin hole that plays an exhaust role on a regular basis to remove the overflow flash around the ejector pin and in the ejector pin hole to avoid blockage. At the same time, this is also one of the methods to avoid the early failure (galling, breaking) of the ejector pin

4 Conclusion

the existence of pores and bubbles in integrated circuit packages has always been a difficult problem in the packaging industry. If we encounter such problems in actual production, we can effectively reduce the scrap rate of plastic packaging products and improve the internal quality of plastic packaging molds by referring to the above methods and combining the specific situation. (end)

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