Baking method before chip packaging

Abstract

Disclosed is a method for baking a chip before packaging, comprising: a heating step configured to heat an oven from room temperature to a first temperature at a first rate within a heating time, open an exhaust outlet of the oven at a first ratio, and fill inert gas at a first flow; the heat preservation step is configured to keep the drying oven at the first temperature according to the set heat preservation time, close an exhaust outlet of the drying oven according to a second proportion and fill the drying oven with inert gas in real time according to a second flow; the cooling step is configured to comprise the steps that heating of the oven is stopped, an exhaust outlet of the oven is closed according to a second proportion, inert gas continues to be injected at a second flow rate, and the temperature in the oven is reduced at a second rate so that the temperature can be reduced from the first temperature to the second temperature, the second rate is smaller than the first rate.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor packaging and testing, and in particular to a baking method before chip packaging. Background Art

[0002] For traditional semiconductor chip packaging, the main process flow includes: wafer thinning step, wafer cutting step, die bonding step, plastic sealing step, electroplating step, cutting (or rib forming) step, testing step, baking step, and packaging step. Depending on the test method, baking can be done before or after the test, but the product needs to be baked before packaging.

[0003] The baking conditions in the baking step are determined by the moisture sensitivity level of the product, which is determined by the product design and application environment. The baking before packaging is mainly to remove moisture from the chip to ensure that the chip can still be soldered to the printed circuit board without quality and reliability problems after a certain period of packaging, transportation and storage.

[0004] The baking step is performed in a high-temperature oven. If there is a large amount of oxygen in the high-temperature oven, the exposed metal parts of the packaged chip will be easily oxidized, especially frame-type packages (QFN, SOP, QFP, etc.). Figure 1 is a diagram showing the appearance of a framework class package. Figure 1 After the frame-packaged products are cut into single chips, the pin cutting surface 1 is directly exposed to the outside, and the cutting surface has not been treated with any anti-oxidation treatment. Generally speaking, the cutting surface is made of copper metal, and the copper metal cutting surface often oxidizes during the baking process, and the cutting surface will turn yellow or dark purple. Correspondingly, the pin tinning surface 2 and the heat sink 3 have undergone a tinning process before cutting, so oxidation will not occur during the baking process. After the chip pin cutting surface 1 is oxidized, it is easy to have poor tinning problems during the subsequent mounting process, affecting the welding performance and reliability of the mounting.

[0005] Based on the above reasons, in the process flow of traditional semiconductor chip packaging, oxygen-free ovens are usually used for production. At the same time, in order to enhance the heat dissipation efficiency, air cooling can be used to accelerate heat dissipation through the air flow in the oven, thereby achieving efficient cooling; in addition, the use of air cooling can reduce the cost of the oven.

[0006] As for the baking method before chip packaging and shipment, since it needs to determine the baking conditions according to the moisture sensitivity level of the product, its baking conditions are different from the parameters in other steps of the chip (for example, the plastic sealing step or the curing step). For example, in the baking step before chip packaging, it is only necessary for the oven to meet the oxygen content in the furnace cavity below 200ppm. On the contrary, the baking used to achieve the functions of curing, activation, welding, stabilization or plastic sealing of the internal structure of the chip often requires a strict oxygen-free environment, that is, an oxygen-free environment with an oxygen content close to 0ppm, and more stringent sealing conditions. Therefore, the baking settings used for other steps are not suitable for the baking of the chip before packaging and shipment in order to remove moisture from the chip. A baking method set for the baking step before packaging is required. Summary of the invention

[0007] The purpose of the present invention is to provide a chip baking method before packaging, which uses an oxygen-free air-cooled oven that can be filled with nitrogen, optimizes the parameters of the oven filled with nitrogen, reasonably adjusts the oven exhaust port settings, and reasonably proportions the nitrogen components filled to solve the problem of oxidation on the cut surface of the chip pins, improves the quality and reliability of the chip mounting process, and at the same time minimizes the operating cost of the baking process.

[0008] According to one aspect of the present disclosure, a method for baking chips before packaging is provided, comprising: a heating step, wherein the heating step is configured to heat an oven from room temperature to a first temperature at a first rate within a heating time, open an exhaust port of the oven at a first ratio, and fill an inert gas at a first flow rate; a heat preservation step, wherein the heat preservation step is configured to keep the oven at the first temperature for a set heat preservation time, close the exhaust port of the oven at a second ratio, and fill the inert gas into the oven in real time at a second flow rate; and a cooling step, wherein the cooling step is configured to include: stopping heating the oven, closing the exhaust port of the oven at a second ratio, continuing to fill the inert gas at a second flow rate, and cooling the temperature inside the oven at a second rate so that the temperature drops from the first temperature to the second temperature, wherein the second rate is less than the first rate.

[0009] According to one aspect of the present disclosure, a method for baking chips before packaging is provided, wherein the cooling step further comprises: after the oven temperature drops to the second temperature, stopping nitrogen filling, and cooling the temperature inside the oven at a third rate so that the temperature of the oven drops from the second temperature to the third temperature, wherein the third rate is configured to be less than the second rate.

[0010] According to one aspect of the present disclosure, a method for baking chips before packaging is provided, wherein the heating step further comprises: opening an exhaust port of an oven at a first ratio within a first opening time period, wherein the first opening time is less than or equal to a heating time.

[0011] According to one aspect of the present disclosure, a baking method before chip packaging is provided, wherein the inert gas includes nitrogen.

[0012] According to one aspect of the present disclosure, a baking method before chip packaging is provided, wherein the first temperature is set to 125°C and the second temperature is set to 80°C.

[0013] According to one aspect of the present disclosure, a baking method before chip packaging is provided, wherein the first rate is set to be within a range of 2 to 3° C. / min, and the second rate is set to be 1.5° C. / min.

[0014] According to one aspect of the present disclosure, a baking method before chip packaging is provided, wherein the first flow rate is set to 100 L / min, and the second flow rate is set to 60 L / min.

[0015] According to one aspect of the present disclosure, a method for baking chips before packaging is provided, wherein the oven is configured as a two-box oven with a cavity size of 710 mm in length, 610 mm in width, and 560 mm in height.

[0016] According to one aspect of the present disclosure, a method for baking a chip before packaging is provided, wherein the packaging type of the chip is a frame-type packaging.

[0017] According to one aspect of the present disclosure, a baking method for chips before packaging is provided, wherein the moisture sensitivity level of the chips is level 3. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and other aspects, features and advantages of the exemplary embodiments of the present disclosure will become more apparent from the following description taken in conjunction with the accompanying drawings, in which:

[0019] Figure 1 is a schematic diagram showing the appearance of a framework class package;

[0020] Figure 2 is a flow chart showing a method for baking chips before packaging according to an embodiment of the present invention;

[0021] Figure 3 is a schematic diagram showing temperature setting in a baking method before chip packaging according to an embodiment of the present invention;

[0022] Figure 4 is a schematic diagram showing the nitrogen flow rate in a chip baking method before packaging according to an embodiment of the present invention; and

[0023] Figure 5It is a schematic diagram showing the opening degree of the exhaust port of the oven in the baking method before chip packaging according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] Before proceeding to the following detailed description, it may be advantageous to set forth definitions of certain words and phrases used throughout this disclosure. The terms "include" and "comprising" and their derivatives mean including, but not limited to. The phrase "at least one," when used with a list of items, means that different combinations of one or more of the listed items may be used, and only one item in the list may be required. For example, "at least one of A, B, C" includes any of the following combinations: A, B, C, A and B, A and C, B and C, A and B and C.

[0025] Definitions for other specific words and phrases are provided throughout this disclosure. Those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior and future uses of such defined words and phrases.

[0026] The various embodiments of the principles of the present disclosure in this patent application document are described below in conjunction with the accompanying drawings for illustration only, and should not be interpreted as limiting the scope of the present disclosure in any way. It will be appreciated by those skilled in the art that the principles of the present disclosure can be implemented in any appropriately arranged system or device. In some cases, the actions described in the present disclosure can be performed in different orders, and the desired results can still be achieved. In addition, the process depicted in the accompanying drawings does not necessarily require the specific order shown or the sequential order to achieve the desired results. In a specific embodiment, multitasking and parallel processing may be advantageous.

[0027] The text and drawings are provided as examples only to help understand the present disclosure. They should not be interpreted as limiting the scope of the claims attached to the present disclosure in any way. Throughout the drawings, the same reference numerals generally indicate the same elements. Although certain embodiments and examples have been provided, based on the contents of the present disclosure, it is clear to those skilled in the art that the embodiments and examples shown may be changed without departing from the scope of the present disclosure.

[0028] The present invention proposes a method for baking chips before packaging and shipment to improve the oxidation of the chip pin cutting surface. The method uses an oxygen-free oven with a nitrogen filling function to bake the chips to discharge the water vapor inside the chips so that the chips meet the requirements for packaging and shipment. During the entire baking process, the oven can automatically fill the furnace cavity with nitrogen in real time. The oven is also provided with an exhaust port to exhaust the air in the oven, and the opening and closing of the exhaust port is set by the oven.

[0029] Figure 2 FIG. 4 is a flow chart showing a method for baking chips before packaging according to an embodiment of the present invention.

[0030] refer to Figure 2 , the chip baking method before packaging according to an embodiment of the present invention comprises: a heating step S111, in which the oven is heated from room temperature to a first temperature, wherein the required time is the heating time, and the exhaust port is opened to the maximum extent so that an inert gas (e.g., nitrogen) is filled in at a larger flow rate (e.g., at a first flow rate) so as to quickly remove the air in the oven and prevent the chip from being oxidized. In the heating step, the rate of temperature rise should not be too fast to avoid adverse effects of thermal shock on the chip. According to an embodiment of the present invention, the temperature can be raised at a first rate or at a rate less than the first rate. According to an embodiment of the present invention, the exhaust port is opened at a first ratio, and this state lasts for a first opening time, and the first opening time is set to be less than the heating time.

[0031] The baking method before chip packaging according to the embodiment of the present invention further includes a heat preservation step S112, in which the oven is kept at a first temperature for a set heat preservation time, wherein in the heat preservation step S112, the exhaust port is closed at a second ratio so that the oven cavity of the oven is close to a closed state, and nitrogen is filled in real time at a lower flow rate at a second flow rate, wherein the second flow rate is less than the first flow rate. According to the embodiment of the present invention, the nitrogen filling amount can be configured to be controlled by a furnace cavity pressure gauge. By closing the exhaust port, a clean and closed condition can be formed to save nitrogen input and save production costs. In addition, by filling nitrogen in real time at the second flow rate at the exhaust port closing device, and controlling the nitrogen filling amount by the furnace cavity pressure gauge, the moisture generated during the baking process can be discharged while maintaining the pressure in the oven. According to the baking method of the embodiment of the present invention, there is no need to make high requirements on the air tightness of the oven, thereby reducing the production cost of the baking method. In addition, by filling nitrogen in real time in the heat preservation step, the moisture in the chip can be further accelerated.

[0032] The chip baking method before packaging according to the embodiment of the present invention further includes a cooling step S113, in which the heating of the oven is stopped, the exhaust port is closed, and nitrogen is continuously charged at a lower flow rate (e.g., a second flow rate); in addition, the oven is cooled by its own internal air cooling device, so that the temperature drops from the insulation temperature (the first temperature) to the second temperature. According to the embodiment of the present invention, in the cooling step, the temperature inside the oven is cooled at a second rate, wherein the second rate is less than the first rate. By setting the second rate to be less than the first rate, the adverse effects of thermal shock on the chip can be further reduced, and the production efficiency and the cooling capacity of the oven are taken into account while ensuring that there is no thermal shock effect in the cooling stage.

[0033] Thereafter, nitrogen filling is stopped, and the temperature of the oven is reduced from the second temperature to the third temperature, and the oven door is opened so that the operator can take the product out of the oven. According to an embodiment of the present invention, the temperature inside the oven is cooled at a third rate so that the temperature of the oven is reduced from the second temperature to the third temperature, wherein the third rate is configured to be less than the second rate. According to an embodiment of the present invention, during the process of cooling from the second temperature to the third temperature, nitrogen filling is stopped and the operation of the cooling device is stopped to further reduce energy consumption and save costs.

[0034] Figure 3 Schematic diagram showing temperature setting in a baking method before chip packaging according to an embodiment of the present invention.

[0035] Figure 4 Schematic diagram showing the nitrogen flow rate in a chip baking method before packaging according to an embodiment of the present invention.

[0036] Figure 5 It is a schematic diagram showing the opening degree of the exhaust port of the oven in the baking method before chip packaging according to an embodiment of the present invention.

[0037] refer to Figure 3 , 4 and 5. In the heating step S111, the first temperature is set to 125°C, the heating time is set to 40min, and in the heating step, the temperature is heated at a first rate, wherein the first rate is set to be within the range of 2-3°C / min. In addition, in the heating step S111, nitrogen is filled at a first flow rate, wherein the first flow rate is set to 100L / min, and at the same time, the degree of opening of the exhaust vent is set at a first ratio, the first ratio is set to 100%, and the opening time is set to 10min, and then the degree of opening of the exhaust vent is set at a second ratio, and the second ratio is set to 0%. It should be understood by those skilled in the art that embodiments of the present invention are not limited to the above parameters. For example, the opening time of opening the exhaust vent at the first ratio can be set to a first opening time, which can be set to be less than or equal to the heating time.

[0038] In the heat preservation step S112, the heat preservation temperature is set to the first temperature, that is, 125°C, and the heat preservation time is set to 8 hours; in addition, nitrogen is provided at a second flow rate, wherein the second flow rate is set to a flow rate of 60L / min to fill the oven in real time. In the heat preservation step S112, the exhaust port opening degree is set at a second ratio, and the second ratio is set to 0%.

[0039] In the cooling step S113, the temperature of the oven is lowered from the first temperature to the second temperature at a second rate, wherein the second temperature is set to 80°C, and the time for lowering the temperature from the first temperature to the second temperature is set to 30 min, and the second rate is set to 1.5°C / min. In the cooling step S113, nitrogen is provided at a second flow rate, wherein the second flow rate is set to a flow rate of 60 L / min, and the exhaust port opening degree is set at a second ratio, and the second ratio is set to 0%.

[0040] According to an embodiment of the present invention, the oven is configured as a two-box oven with a cavity length of 710 mm, a width of 610 mm, and a height of 560 mm. The oven temperature range is: RT (room temperature) ~ 250°C, and the oven temperature uniformity is configured to be ±1.5% (in the case of an empty oven) to meet the baking requirements of the entire batch of chips. In addition, the temperature control accuracy of the oven is configured to be ±0.3%.

[0041] According to an embodiment of the present invention, the nitrogen gas filled into the oven is high-purity nitrogen, and the purity of the nitrogen gas is configured to be above 99.999% (volume fraction).

[0042] According to an embodiment of the present invention, the chip packaging type is a frame-type packaging, and preferably, the chip packaging type is a QFN packaging.

[0043] According to an embodiment of the present invention, the frame used in the chip packaging is a copper frame.

[0044] According to an embodiment of the present invention, the humidity sensitivity level of the chip is level 3.

[0045] According to an embodiment of the present invention, the oven type is set to be an air-cooled oxygen-free oven, and the oven is set to be able to be filled with nitrogen in real time. In addition, the cooling method of the oven is set to an air-cooled method, and the oven is also provided with an exhaust vent.

[0046] According to an embodiment of the present invention, the oven is configured as a two-box oven with a cavity size of 710 mm in length, 610 mm in width, and 560 mm in height.

[0047] According to an embodiment of the present invention, the oxygen content in the oven during the oven insulation process is set to be less than 200 ppm.

[0048] According to an embodiment of the present invention, after being processed by a baking method including a heating step, a heat preservation step, and a cooling step, the oxidation degree of the pin cutting surface of the frame-type packaged chip is significantly reduced, and yellow or purple oxidation marks are eliminated.

[0049] Those skilled in the art will appreciate that the various illustrative logic blocks, modules, circuits, and steps described in this disclosure may be implemented as hardware, software, or a combination of the two. Whether such a function set is implemented as hardware or software depends on the specific application and the design constraints imposed on the overall system. The technician may implement the described function set in different ways for each specific application, but such design decisions should not be interpreted as causing a departure from the scope of this disclosure.

[0050] The above-mentioned embodiments of the present disclosure are only for easy description and help comprehensive understanding of the present disclosure, and are not intended to limit the scope of the present disclosure. Therefore, it should be understood that, in addition to the above-mentioned embodiments disclosed herein, all modifications and changes or forms of modifications and changes derived from the technical concept of the present disclosure fall within the scope of the present disclosure.

Claims

1. A method for baking a chip before packaging, comprising: A heating step, wherein the heating step is configured to heat the oven from room temperature to a first temperature at a first rate within a heating time, open an exhaust port of the oven at a first ratio, and fill the oven with an inert gas at a first flow rate; a heat preservation step, wherein the heat preservation step is configured to maintain the oven at a first temperature for a set heat preservation time, close the exhaust port of the oven at a second ratio, and fill the oven with an inert gas at a second flow rate in real time; as well as A cooling step, wherein the cooling step is configured to include: stopping heating the oven, closing the exhaust port of the oven at a second ratio, continuing to fill the inert gas at a second flow rate, and cooling the temperature inside the oven at a second rate so that the temperature drops from the first temperature to the second temperature, wherein the second rate is less than the first rate.

2. The method for baking chips before packaging according to claim 1, wherein: The cooling step further includes: after the oven temperature drops to the second temperature, stopping nitrogen filling, and cooling the temperature inside the oven at a third rate so that the temperature of the oven drops from the second temperature to a third temperature, wherein the third rate is configured to be less than the second rate.

3. The method for baking chips before packaging according to claim 1, wherein: The heating step further includes: opening the exhaust port of the oven at a first ratio within a first opening time period, wherein the first opening time is less than or equal to the heating time.

4. The method for baking chips before packaging according to claim 1, wherein: The inert gas includes nitrogen.

5. The method for baking chips before packaging according to claim 1, wherein: The first temperature was set to 125°C, and the second temperature was set to 80°C.

6. The method for baking chips before packaging according to claim 1, wherein: The first rate is set to be in the range of 2-3°C / min, and the second rate is set to be 1.5°C / min.

7. The method for baking chips before packaging according to claim 1, wherein: The first flow rate is set to 100 L / min, and the second flow rate is set to 60 L / min.

8. The method for baking chips before packaging according to claim 1, wherein: The oven is configured as a two-box oven with a cavity size of 710 mm in length, 610 mm in width, and 560 mm in height.

9. The method for baking chips before packaging according to claim 1, wherein: The packaging type of the chip is frame packaging.

10. The method for baking chips before packaging according to claim 1, wherein: The humidity sensitivity level of the chip is level 3.

Images