Interpretation of common defects in EMC packaging forming and its countermeasures

Plastic packaging has become the mainstream of current microelectronic packaging with its unique advantages, accounting for more than 95% of the packaging market. The wide application of plastic packaging products has brought unprecedented development to plastic packaging, but almost all plastic molding products have defects in forming defects, whether using advanced transfer molding or traditional single injection molding. Packaging is not completely avoided. In comparison, the traditional plastic sealing mold has a large probability of forming defects, and the types are also large. The larger the size, the greater the probability of occurrence. The quality of plastic products is mainly determined by four factors: A, EMC performance, including gelation time, viscosity, fluidity, mold release, adhesion, moisture resistance, heat resistance, flashing properties , stress, strength, modulus, etc.; B, mold, mainly including the degree of matching between the runner, gate, cavity, exhaust port design and lead frame design; C, package form, different package forms often appear different Defects, so optimizing the design of the package form will greatly reduce the occurrence of defective defects; D, process parameters, mainly including mold clamping pressure, injection pressure, injection speed, preheating temperature, mold temperature, curing time and so on.

The following mainly analyzes and studies the causes of defects commonly encountered in plastic molding, and proposes corresponding effective and feasible solutions and countermeasures.

1. Package forming is not filled and its countermeasures

There are two main cases of package forming and unfilling: one is the tendency to be unfilled, mainly due to the mismatch between the packaging process and EMC performance parameters; one is random unfilled, mainly due to mold cleaning. Improper, the insoluble impurities in the EMC are too large, the mold feed port is too small, etc., causing blockage of the mold gate. From the perspective of package form, unfilled phenomenon is more likely to occur in DIP and QFP. From the aspect of appearance, DIP is not filled mainly in the form of completely unfilled and partially unfilled, and QFP mainly has corners not filled. The main reasons for unfilling and their countermeasures:

(1) There is a tendency to be unfilled due to the mold temperature being too high, or the packaging process does not match the EMC performance parameters. After the preheating, the reaction speed of the EMC is increased at a high temperature, so that the gelation time of the EMC is relatively short, and the fluidity is deteriorated. When the cavity is not completely filled, the viscosity of the EMC is sharply increased, and the flow resistance is also increased. As a result, a good filling is not obtained, thereby forming a tendency to be unfilled. This phenomenon is more likely to occur in VLSI packages, because the amount of EMC per mode of these large-scale circuits tends to be relatively large. In order to achieve uniform heating effect in a short time, the set temperature is often high, so it is easy to produce. This is not filled. For this kind of trending unfilling, which is mainly caused by insufficient EMC fluidity, it can be used to increase the preheating temperature of EMC to make it evenly heated; increase the injection pressure and speed, and accelerate the flow rate of EMC; The temperature is used to slow down the reaction rate and relatively extend the gelation time of the EMC to achieve a full filling effect.

(2) Due to the blockage of the mold gate, the EMC cannot be effectively injected, and the vent hole is blocked due to improper cleaning of the mold, which may cause unfilling, and the position of the unfilled in the mold is also irregular. In particular, in a small package, since the gate and the exhaust port are relatively small, it is most likely to cause clogging and unfilling. For this unfilled, the tool can be used to remove the blockage and apply a small amount of release agent, and after each mold package, the EMC curing material on the barrel and the mold should be removed with a brush.

(3) Although the packaging process and the performance parameters of the EMC are well matched, the fluidity of the EMC is lowered due to improper storage or expiration, and the viscosity is too large or the gelation time is too short, which may cause poor filling. The solution is to choose EMC with suitable viscosity and gel time, and keep it in accordance with EMC's storage and use requirements.

(4) Unfilled due to insufficient EMC usage. This situation usually occurs when replacing EMC, package type or mold replacement. The solution is also simple. Just select the EMC quantity that matches the package type and mold. Can be solved, but the amount should not be too much or too little.

2, package forming pores and countermeasures

Porosity is the most common defect during package forming. According to the position where the pores are formed on the plastic body, the inner pores and the outer pores can be divided, and the outer pores can be further divided into the top pores and the gate pores. The air hole not only seriously affects the appearance of the plastic body, but also directly affects the reliability of the plastic sealing device, especially the internal air hole. The common pores are mainly external pores. The internal pores cannot be directly seen. They must be observed by X-ray apparatus, and the smaller internal pores Bp can not be seen clearly by X-rays. This also brings great resistance to pore defects. difficult. Then, in order to solve the problem of porosity defects, it is necessary to carefully study the formation process of various types of pores. However, strictly speaking, the pores cannot be completely eliminated, and measures can only be taken to improve them, and the pore defects are controlled within the scope of good products.

From the surface of the pores, the reason for the formation seems to be very simple, but the residual gas in the cavity is not effectively discharged. In fact, there are many factors causing porosity defects, mainly in the following aspects: A. Packaging materials, mainly including EMC gelation time, viscosity, fluidity, volatile matter content, moisture content, air content, and cake density. , the diameter of the cake does not match the diameter of the material; B, the mold, and the shape of the barrel, the shape and arrangement of the cavity, the shape and position of the gate and the exhaust port; C, packaging technology, Mainly related to preheating temperature, mold temperature, injection speed, injection pressure, injection time and so on.