Manufacturing method of flip packaging support
By electroplating tin on the functional pads of the flip chip and combining it with the hot pressing technology of the cup plate, the problems of chip-pad alignment and solder filling in the flip chip are solved, achieving high-density and high-performance packaging effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-19
- Publication Date
- 2026-03-13
AI Technical Summary
Existing flip-chip technology cannot achieve precise alignment between the chip and the pad and effective solder filling when setting up the cup structure, thus failing to overcome the limitations of flip-chip packaging with a cup.
By pre-plating tin on the functional pads, the cup-shaped piece and the substrate are combined in one piece. The cup-shaped piece is pressed onto the substrate surface by hot pressing technology, and a tin-plated layer is covered on the functional pads. This eliminates the traditional soldering step and completes the die bonding operation of the chip by reflow soldering.
It achieves a perfect combination of flip-chip technology and cup structure, improving the alignment accuracy and soldering reliability of the chip and pad, and is suitable for high-density, high-performance semiconductor packaging.
Smart Images
Figure CN121665783A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of packaging bracket technology, specifically a method for manufacturing a flip-chip packaging bracket. Background Technology
[0002] In semiconductor / optoelectronic packaging, there are two core chip-support connection methods: upright and flip-chip. The essential difference lies in the chip placement direction and electrode interconnection mechanism, which in turn affects performance, cost, and application scenarios.
[0003] In the upright mounting, the active side of the chip faces upward, and the chip electrodes are connected to the external pins of the bracket via wire bonding; suitable for scenarios that pursue low cost and low complexity, and are suitable for low power, low frequency, and size insensitive applications;
[0004] In flip-chip design, the chip flips 180° with the active side facing down, directly aligning with the pads of the bracket for a leadless direct connection. This design is suitable for scenarios requiring high performance, high heat dissipation, and small size, as well as high power, high frequency, and high density integration.
[0005] Because flip-chip bonding pads are smaller, and considering the difficulty of chip soldering, existing flip-chip bonding pads have a "cupless" structure. The bonding method usually involves pre-filling the pads with bump solder, then flipping the chip to make it contact the bump solder, and then heating it through reflow soldering to melt the solder, using capillary action to fill the gap between the bumps and the pads.
[0006] However, the above method is only applicable to the "cupless" structure. Because the diameter of the opening is very small after the cup is set, the method used cannot form bump solder on the pad, and it is difficult to align the chip with the pad. Therefore, it has always been impossible to break through the flip-chip bracket with cup. Summary of the Invention
[0007] The purpose of this invention is to provide a method for manufacturing a flip-chip packaging bracket to solve the problems mentioned in the background art.
[0008] To achieve the above objectives, the present invention provides the following technical solution:
[0009] A method for manufacturing a flip-chip packaging bracket includes a substrate and an integrally molded cup-shaped plate;
[0010] The first step is to form several pad units on the surface of the substrate. Each pad unit contains several functional pads with a spacing of 40μm-50μm between them. Several pins are formed at the bottom of the pad unit to communicate with the functional pads.
[0011] The second step is to make bowl-cup pieces, each of which contains several cups, and each cup corresponds one-to-one with each pad unit;
[0012] The third step is to press the cup sheet onto the surface of the substrate by hot pressing, so that several functional pads are located at the bottom of the cup body;
[0013] The fourth step is to electroplat the surface of the functional pads with tin so that each functional pad is covered with a tin plating layer.
[0014] The fifth step is to clean the electroplated packaging bracket.
[0015] A further technical solution, based on the fourth step, involves first performing silver plating before tin plating, so that a silver plating layer is formed on both the pins and functional pads. Then, a dry film is applied to the bottom surface of the substrate to cover and protect the silver plating layer on several pins. Tin plating is then performed, and finally the dry film is removed.
[0016] A further technical solution, based on the third step, involves applying a bonding adhesive to the side of the cup sheet that is close to the substrate.
[0017] In a further technical solution, the bowl / cup sheet is made of black core material TG.
[0018] A further technical solution is that the epoxy resin used for pressing is less than 0.05mm overflow in the cup body.
[0019] In a further technical solution, the height of the cup body is 0.76mm, and the inner diameter of the cup body opening is 1mm.
[0020] The beneficial effects of this invention are:
[0021] This invention innovatively replaces the traditional soldering solution by pre-plating tin on the functional pads. When bonding the chip, only flux needs to be injected into the cup, so that the chip can be placed upside down in the narrow space of the cup. The die bonding operation is then precisely completed through reflow soldering, filling the technical gap that makes it impossible to bond the chip to the cup in flip-chip bonding.
[0022] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description
[0023] Figure 1 : Flowchart of the present invention.
[0024] Figure 2 : A structural diagram of the inverted bracket of the present invention. Detailed Implementation
[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.
[0026] The cup-shaped structure in the packaging lead frame has irreplaceable optical advantages in optoelectronic packaging. Traditional cupless flip-chip lead frames have the following limitations: low light utilization: side-emitting light from the chip cannot be effectively collected, resulting in light efficiency loss of more than 30%; difficult to control the light emission angle: lack of directional reflection structure, resulting in poor beam uniformity; low phosphor coating precision: direct coating easily causes uneven color temperature.
[0027] In existing technologies, traditional flip-chip requires a flat soldering surface, while the cup body is a three-dimensional structure. Traditional bump soldering requires an open space for operation, which the narrow opening of the cup body cannot meet. Moreover, the alignment accuracy between the cup body and the micron-level solder pads is extremely high, exceeding the capabilities of conventional equipment. These factors limit the use of a cup body structure in flip-chip carriers.
[0028] Please refer to Figure 1-2 ;
[0029] The present invention aims to disclose an inverted bracket implementation scheme with a cup body 3, specifically including a substrate 1 and an integrally formed bowl-cup piece;
[0030] The first step involves using an epoxy-based material or glass fiber as the substrate, with a thickness of 0.2mm-0.5mm. Through-holes are formed by laser drilling to serve as interlayer conduction and positioning references. Then, copper is plated on both sides of the substrate, with a copper layer thickness of 18-35μm. The copper passes through the through-holes, connecting the copper layers on both sides. After exposure, development, etching, and other steps, several pad units are formed on the substrate 1. Each pad unit contains several functional pads 2. Then, the substrate is ultrasonically cleaned with deionized water (resistivity ≥18MΩ·cm) for 5 minutes to remove residual etchant. The spacing between the functional pads 2 is 40μm-50μm. Several pins 7 are formed at the bottom of the pad unit to connect with the functional pads 2.
[0031] The second step is to manufacture the bowl-cup sheet by injection molding. Each bowl-cup sheet contains several cup bodies 3, and each cup body 3 corresponds one-to-one with each pad unit. Preferably, it is formed by hot pressing with a precision mold, and the inner wall of the cup is polished to Ra≤0.1μm to enhance the light reflectivity.
[0032] The third step is to press the cup sheet 3 onto the surface of the substrate 1 by hot pressing, so that several functional pads 2 are located at the bottom of the cup body 3. Of course, according to the existing technology, the substrate 1 needs to be drilled in advance to form positioning holes for precise alignment of the substrate 1 and the cup sheet during pressing, so as to ensure the relative positional accuracy of the cup body 2, the circuit layer and the pressing adhesive.
[0033] To improve the hot pressing effect, a segmented pressing process is adopted, which is divided into three stages: pre-pressing, main pressing and slow cooling.
[0034] The pre-compression temperature is 80℃-100℃, the pressure is 50kPa-80kPa, and the time is 30 seconds-60 seconds to initially fix the cup body 3 and release the initial stress;
[0035] The main pressure temperature is 150℃-160℃, the pressure is 150kPa-200kPa, and the time is 60 seconds-90 seconds to complete the metal bonding and interface fusion.
[0036] The slow cooling temperature is 100℃-80℃, the pressure is 50kPa-30kPa, and the time is 120 seconds-180 seconds, which reduces thermal shock by gradient cooling.
[0037] In addition, the cup body 3 is designed to accommodate the flipped chip 6, so there is no problem of not being able to accommodate the chip 6. Preferably, the height of the cup body 3 is 0.76mm and the inner diameter of the opening of the cup body 3 is 1mm.
[0038] In the fourth step, after the cup plate 3 is combined with the substrate 1, several functional pads 2 are located at the bottom of the cup body 3, and the copper surface at the bottom of the cup body is exposed. The copper surface of the functional pads is electroplated with tin, so that each functional pad is covered with a tin plating layer 4. Preferably, the uniformity of the tin plating layer 4 directly affects the soldering yield. If the plating layer thickness is uneven, it may lead to poor soldering or short circuit. Therefore, pulse electroplating technology can be used to improve the uniformity of the plating layer by adjusting the current waveform. The current density of pulse electroplating should be controlled at 1.5-3.5A / dm², and the frequency should be 50-200Hz to ensure that the thickness of the tin plating layer 4 is uniform (3-8μm).
[0039] The fifth step is to clean the electroplated packaging bracket.
[0040] Based on the above steps, it can be seen that the gap between the functional pads 2 is very small. Before the cup body 3 is pressed, the space around the functional pads 2 is open, which can be filled with solder. However, after the cup body 3 is added, the solder filling depends on the dispensing equipment, which is difficult to control precisely in a narrow space. Therefore, the traditional dispensing step can be omitted by pre-plating tin on the functional pads 2 to avoid space limitations. When bonding with the chip 6 is required, dehumidification is performed first to keep the package bracket dry. Then, flux is injected into the cup body 3, and the chip 6 is placed upside down on the functional pads 2. The flux and tin plating layer 4 are melted by reflow soldering. After natural cooling, the die bonding is completed. Finally, the process is carried out by dispensing, curing, cutting, and photolithography.
[0041] In a countermeasure, an attempt was made to perform a die bonding operation first, and then press the cup 3 onto the pad unit. However, since the process of pressing the cup 3 onto the pad unit takes a long time and the temperature is high, the high temperature generated during the pressing process will damage the chip 6, so this method fails.
[0042] This invention innovatively replaces the traditional soldering solution by pre-plating tin on the functional pads 2. When bonding the chip 6, only flux needs to be injected into the cup 3, so that the chip 6 can be placed upside down in the narrow space of the cup 3. The die bonding operation is precisely completed through reflow soldering, realizing a perfect combination of flip-chip technology and cup structure. This breakthrough not only fills the technological gap in the industry, but also provides a development direction for the next generation of high-density, high-performance semiconductor packaging.
[0043] This invention provides a further extension of the above-described embodiments;
[0044] In traditional processes, when both sides are tinned, the tin layer on the chip side is prone to melting during reflow soldering, leading to short circuits. To address this issue, this technical solution employs a different electroplating process. More specifically, based on the fourth step, silver plating is performed before tin plating: a silver plating layer 5 covers the copper surface of pin 7. Preferably, the functional pad 3 is not covered during silver plating, and a silver plating layer 5 is pre-formed on its copper surface. Then, a dry film is applied to the bottom of the substrate 1 to cover and protect the silver plating layer 5 on several pins 7. Tin plating is then performed, and finally, the dry film is removed. The tin plating layer 4 on the package side is dedicated to bonding the chip, and its melting point matches the reflow soldering process. The silver plating layer 5 on the pin 7 has a melting point as high as 961°C, which is much higher than the reflow soldering temperature. This perfectly avoids the serious defects caused by the melting of the tin layer on the chip side during packaging of products with tinning on both sides. The step-by-step electroplating solution not only improves packaging reliability but also provides technical support for high-frequency and high-power applications.
[0045] More specifically, the tin plating process can completely cover the copper oxide layer of the functional pads, providing a complete soldering interface. It also has the ability to absorb stress through plastic deformation, which can absorb thermal stress through micro-plastic deformation, preventing the solder joints from cracking due to stress concentration and avoiding cold solder joints.
[0046] In addition, assuming that the copper surfaces of the functional pads and pins are tin-plated, the temperature generated during chip bonding will cause the tin surface of the bottom pins to melt, increasing the risk of poor soldering between the pins and the PCB board. However, in this embodiment, the copper surface of the pins is plated with silver layer 5, and the temperature during chip bonding is not high enough to melt the silver layer 5, thus preventing poor soldering.
[0047] In this embodiment of the invention, based on the third step, a bonding adhesive is applied to the side of the cup sheet that is close to the substrate 1, and the hot pressing temperature is 130℃-200℃;
[0048] After chip 6 is bonded to the flip-chip substrate, a large amount of heat is generated during use and conducted to the functional pads 2 and the cup body 3. The cup body 3, traditionally injection molded, deforms under heat, affecting its airtightness. In this embodiment, the cup body is made of black core material (TG). The TG value of black core material is typically higher than that of ordinary substrates, reaching over 170°C. The higher the TG value, the stronger the material's ability to maintain rigidity and dimensional stability at high temperatures. High-TG black core material is less prone to deformation under heat, thus ensuring that the encapsulation substrate remains undeformed during operation and maintaining good airtightness. Preferably, the bonding adhesive is epoxy resin, and the viscosity of the epoxy resin bonding adhesive should be ≤500 cP to ensure uniform flow of the adhesive during hot pressing, avoiding local accumulation or voids, thereby improving bonding strength. Furthermore, the cup body is made of black core material (TG). This material works synergistically with epoxy resin bonding adhesive: the high-temperature stability of the black core material prevents the cup plate from deforming due to heat, while the epoxy resin provides flexible bonding, together ensuring the dimensional stability and airtightness of the encapsulation bracket under high-temperature working environment; the epoxy resin adhesive forms a strong bond under hot pressing process, and combined with the rigidity of the black core material TG, the bracket can withstand the thermomechanical stress under high frequency and high power scenarios, with less than 0.05mm of adhesive overflow inside the cup body 3.
[0049] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.
[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for manufacturing a flip-chip packaging bracket, characterized in that: Includes a substrate and an integrally molded bowl / cup sheet; The first step is to form several pad units on the surface of the substrate. Each pad unit contains several functional pads with a spacing of 40μm-50μm between them. Several pins are formed at the bottom of the pad unit to communicate with the functional pads. The second step is to make bowl-cup pieces, each of which contains several cups, and each cup corresponds one-to-one with each pad unit; The third step is to press the cup sheet onto the surface of the substrate by hot pressing, so that several functional pads are located at the bottom of the cup body; The fourth step is to electroplat the surface of the functional pads with tin so that each functional pad is covered with a tin plating layer. The fifth step is to clean the electroplated packaging bracket.
2. The method for manufacturing a flip-chip packaging bracket according to claim 1, characterized in that: Based on the fourth step, before performing tin plating, silver plating is performed first to form a silver plating layer on the pins and functional pads. Then, a dry film is covered on the bottom surface of the substrate to cover several pins and protect the silver plating layer. Tin plating is then performed, and finally the dry film is removed.
3. The method for manufacturing a flip-chip packaging bracket according to claim 1, characterized in that: Based on the third step, a bonding adhesive is applied to the side of the cup sheet that is close to the substrate.
4. The method for manufacturing a flip-chip packaging bracket according to claim 1, characterized in that: The bowl / cup sheet is made of black core material TG.
5. The method for manufacturing a flip-chip packaging bracket according to claim 4, characterized in that: The epoxy resin used for pressing has an overflow of less than 0.05mm inside the cup.
6. The method for manufacturing a flip-chip packaging bracket according to claim 1, characterized in that: The cup body has a height of 0.76 mm and an inner diameter of 1 mm at the opening.