A flip chip packaging process method

Abstract

The application discloses a flip chip packaging process method, and belongs to the flip chip packaging technical field. The application places a tin ball on a support base with a groove for ball placement on the back of a substrate, and the base is made of metal material, which can ensure that heat is quickly transferred to the tin ball. The surface plating layer is made of material which is not easy to stick to solder, which can prevent the tin ball from sticking to the groove after melting. In addition, the groove of the base is in a mode similar to a U-shaped groove, the diameter of the slot is slightly larger than the diameter of the tin ball by 10-30 um, and the depth is 80%-90% of the diameter of the tin ball, so that the tin ball can be smoothly placed in the groove. In addition, compared with the conventional BGA flip chip packaging method, the application changes the two reflow soldering into one reflow soldering, which greatly reduces the residence time of the chip in the high temperature zone, thereby being beneficial to reducing the influence of high temperature thermal effect on the performance and reliability of part of the chip.

Description

Technical Field

[0001] This invention relates to the field of flip chip packaging technology, and more particularly to a flip chip packaging process method. Background Technology

[0002] As chip internal linewidths become smaller and smaller, from tens of nanometers to 5-7nm, they become increasingly sensitive to temperature. If some chips are exposed to high temperatures for too long, abnormalities may occur, such as drift in the operating point of the internal transistor amplifier, changes in the transistor current amplification factor, and changes in the characteristic curve, which will affect the performance and quality of the chip.

[0003] The conventional production process requires at least two reflow soldering processes. The first reflow is after the die is flip-chip mounted onto the substrate, and the second reflow is when the solder balls are attached to the back of the substrate. The solder balls are melted and soldered at a high temperature of 240 to 260 degrees Celsius. Each high-temperature zone is held for 60 to 90 seconds, and the two processes together take about 120 to 180 seconds. This duration not only affects the performance of some chips, but may also pose a potential reliability risk.

[0004] Therefore, there is an urgent need to invent a new flip-chip packaging process to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to address the deficiencies in the existing technology by proposing a flip-chip packaging process method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A flip-chip packaging process includes the following steps:

[0008] Step 1: Using a ball-forming machine, place the solder balls onto the grooved support base;

[0009] Step 2: Place the substrate on the surface of the solder ball and fix the substrate to the base using grippers or positioning pins;

[0010] Step 3: Perform front-side die bonding on the substrate using conventional flip-chip bonding technology;

[0011] Step 4: Simultaneously perform high-temperature reflow soldering on the substrate and the fixture.

[0012] Step 5: Apply adhesive to wrap and seal the solder balls of the die with adhesive;

[0013] Step 6: Remove the fixture to complete the entire surface mount and reflow soldering process.

[0014] Furthermore, the process method further includes:

[0015] Several grooves are pre-fabricated on the surface of the base. The position design of the grooves needs to take into account the difference in the coefficient of expansion between the substrate and the base at high temperature. The position of the grooves is calculated and determined based on the coefficient difference to ensure that the position of the grooves is aligned with the solder ball soldering position on the back of the substrate at high temperature.

[0016] Furthermore, the size of the groove is 10-30 μm larger than the diameter of the solder ball, and the depth of the groove is 80%-90% of the diameter of the solder ball.

[0017] Furthermore, during operation, the ball-planting machine changes the conventional ball-planting process on the circuit board surface to ball-planting on the base surface, and automatically places the solder balls into the grooves on the base surface.

[0018] Furthermore, during the high-temperature reflow soldering, the solder balls will automatically align with the solder pads on the back of the substrate.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] This application proposes a flip-chip packaging process that uses a grooved support base to place solder balls for back-side bonding on a substrate. The base is made of metal to ensure rapid heat transfer to the solder balls, and the surface plating is made of a material that prevents solder from sticking to the groove after melting. The groove of the base is designed in a U-shape, with the groove opening diameter slightly larger than the solder ball diameter by 10-30 μm and the depth being 80%-90% of the solder ball diameter, thus ensuring that the solder balls can be smoothly placed into the groove. Furthermore, compared to conventional BGA flip-chip packaging methods, this invention changes two reflow soldering processes to one, significantly reducing the time the chip spends in the high-temperature region, thereby helping to reduce the impact of high-temperature thermal effects on the performance and reliability of some chips. Attached Figure Description

[0021] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0022] Figure 1 This is an overall flowchart of a flip-chip packaging process method in the first embodiment;

[0023] Figure 2 This is a schematic diagram of the packaging structure of a flip-chip packaging process in the first embodiment;

[0024] Figure 3 This is an overall flowchart of the conventional BGA flip chip packaging method in the second embodiment;

[0025] Figure 4 This is a schematic diagram of the packaging structure of the conventional BGA flip chip packaging method in the second embodiment. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0027] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship 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 limitations on this invention.

[0028] Example 1

[0029] Reference Figure 1-2 This embodiment discloses a flip-chip packaging process method, including the following steps:

[0030] Step 1: Using a ball-forming machine, place the solder balls onto the grooved support base;

[0031] In one embodiment, the process method further includes:

[0032] Several grooves are pre-fabricated on the surface of the base. The position design of the grooves needs to take into account the difference in the coefficient of expansion between the substrate and the base at high temperature. The position of the grooves is calculated and determined based on the coefficient difference to ensure that the position of the grooves is aligned with the solder ball soldering position on the back of the substrate at high temperature.

[0033] Specifically, the base is made of metal, which can ensure that heat is quickly transferred to the solder ball. The surface plating is made of a material that does not easily stick to the solder, which can prevent the solder ball from sticking to the groove after melting. The groove of the base can adopt a U-shaped groove pattern. The size of the groove is 10-30 μm larger than the diameter of the solder ball, and the depth of the groove is 80%-90% of the diameter of the solder ball.

[0034] To illustrate the above description, since a small portion of the solder ball protrudes outside the groove after it is placed in the groove, assuming the solder ball diameter is 300 μm, the groove can be designed to be 310–330 μm according to the present invention to ensure that the solder ball can be smoothly placed in the groove; the depth is 240 μm–270 μm, and a small portion of the top of the solder ball protrudes outside the groove.

[0035] Specifically, during operation, the ball-planting machine changes the conventional ball-planting process on the circuit board surface to ball-planting on the base surface, and automatically places the solder balls into the grooves on the base surface.

[0036] Step 2: Place the substrate on the surface of the solder ball and fix the substrate to the base using grippers or positioning pins;

[0037] Step 3: Perform front-side die bonding on the substrate using conventional flip-chip bonding technology;

[0038] Step 4: Simultaneously perform high-temperature reflow soldering on the substrate and the fixture.

[0039] Specifically, since the groove and the solder ball pad on the back of the substrate are in the same position, the solder ball will automatically align with the solder ball on the back of the substrate during the high-temperature reflow soldering; during the high-temperature reflow soldering, it can be ensured that the solder ball automatically wets the copper pad or gold-plated pad of the solder ball on the back of the substrate.

[0040] Step 5: Apply adhesive to wrap and seal the solder balls of the die with adhesive;

[0041] Step 6: Remove the fixture to complete the entire surface mount and reflow soldering process.

[0042] Example 2

[0043] Reference Figure 3-4 This embodiment will introduce a conventional BGA flip chip packaging method, including the following steps:

[0044] Step 1: The substrate is fitted with front-side die using a conventional flip-chip bonding process;

[0045] Step 2: First reflow soldering, the high-temperature zone is generally between 240 and 280 degrees Celsius;

[0046] Step 3: Use a dispensing machine to fill the bottom, completely filling and wrapping the chip solder joints;

[0047] Step 4: With the back side of the substrate facing up, place the balls on the substrate surface;

[0048] Step 5: Second reflow soldering, the high-temperature zone is generally between 240 and 280 degrees Celsius;

[0049] In this embodiment, the method performs subsequent cutting, inspection, and other packaging processes after two reflow soldering cycles.

[0050] In one embodiment, to verify the technical effect of this application, this embodiment will compare the chip operation time effect in a high-temperature environment between a flip-chip packaging process method of Embodiment 1 and a conventional BGA flip-chip packaging method of Embodiment 2. The specific data are shown in the table below:

[0051] Table 1: Comparison of chip operating time performance in high-temperature environments

[0052]

[0053] As can be seen from the table above, compared with the conventional BGA flip chip packaging method, this application significantly reduces the time the chip spends in the high-temperature region by changing the two reflow soldering processes to one reflow soldering process. This helps to reduce the impact of high-temperature thermal effects on the performance and reliability of some chips.

[0054] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A flip-chip packaging process, characterized in that, Includes the following steps: Step 1: Using a ball-forming machine, place the solder balls onto the grooved support base; Step 2: Place the substrate on the surface of the solder ball and fix the substrate to the base using grippers or positioning pins; Step 3: Perform front-side die bonding on the substrate using conventional flip-chip bonding technology; Step 4: Simultaneously perform high-temperature reflow soldering on the substrate and the fixture. Step 5: Apply adhesive to wrap and seal the solder balls of the die with adhesive; Step 6: Remove the fixture to complete the entire surface mount and reflow soldering process; The process method further includes: Several grooves are pre-made on the surface of the base. The position design of the grooves needs to take into account the difference in the coefficient of expansion of the substrate and the base at high temperature. The position of the grooves is calculated and determined based on the coefficient difference to ensure that the position of the grooves is aligned with the solder ball soldering position on the back of the substrate at high temperature. The groove is 10-30 μm larger than the diameter of the solder ball, and the groove depth is 80%-90% of the diameter of the solder ball.

2. The flip-chip packaging process method according to claim 1, characterized in that, During operation, the ball-planting machine changes the conventional ball-planting process on the circuit board surface to ball-planting on the base surface, and automatically places the solder balls into the grooves on the base surface.

3. The flip-chip packaging process method according to claim 1, characterized in that, During the high-temperature reflow soldering process, the solder balls will automatically align with the solder pads on the back of the substrate.

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