Patent Application
20240047255
Embodiments of the present disclosure relate generally to semiconductor processing, and more particularly to solder reflow system.
The semiconductor industry has experienced rapid growth due to ongoing improvements in the integration density of a variety of electronic components (e.g., transistors, diodes, resistors, capacitors, etc.). For the most part, improvement in integration density has resulted from iterative reduction of minimum feature size, which allows more components to be integrated into a given area.
While some integrated device manufacturers (IDMs) design and manufacture integrated circuits (IC) themselves, fabless semiconductor companies outsource semiconductor fabrication to semiconductor fabrication plants or foundries. Semiconductor fabrication consists of a series of processes in which a device structure is manufactured by applying a series of layers onto a substrate. This involves the deposition and removal of various dielectric, semiconductor, and metal layers. The areas of the layer that are to be deposited or removed are controlled through photolithography. Each deposition and removal process is generally followed by cleaning as well as inspection steps. Therefore, both IDMs and foundries rely on numerous semiconductor equipment and semiconductor fabrication materials, often provided by vendors. There is always a need for customizing or improving those semiconductor equipment and semiconductor fabrication materials, which results in more flexibility, reliability, and cost-effectiveness.
Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.
The following disclosure provides many different embodiments, or examples, for implementing different features of the subject matter provided. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.
Some embodiments of the disclosure are described. Additional operations can be provided before, during, and/or after the stages described in these embodiments. Some of the stages that are described can be replaced or eliminated for different embodiments. Some of the features described below can be replaced or eliminated and additional features can be added for different embodiments. Although some embodiments are discussed with operations performed in a particular order, these operations may be performed in another logical order.
Overview
Packaging technologies were once considered just back-end processes. Times have changed. Computing workloads have evolved more over the past decade than perhaps the previous four decades. Cloud computing, big data analytics, artificial intelligence (AI), neural network training, AI inferencing, mobile computing on advanced smartphones, and even self-driving cars are all pushing the computing envelope. Modern workloads have brought packaging technologies to the forefront of innovation, and they are critical to a product's performance, function, and cost. These modern workloads have pushed the product design to embrace a more holistic approach for optimization at the system level.
Reflow soldering (sometimes also referred to as a “reflow process”) is a process widely used in various packaging technologies. In a reflow soldering process, a solder paste (i.e., a sticky mixture of powdered solder and flux) is used to temporarily attach one or thousands of tiny electrical components to their contact pads, after which the entire assembly is subjected to controlled heat. The solder paste reflows in a molten state, creating permanent solder joints. Heating may be accomplished by passing the assembly through a solder reflow oven (sometimes also referred to as a “reflow oven”). An example of solder reflow ovens is a solder reflow oven manufactured by Heller Industries, and the reflow process may sometimes be referred to as a “Heller reflow process.”
Reflow soldering with long industrial convection ovens is a common method of soldering surface mount technology (SMT) components to a printed circuit board (PCB). Each segment of the oven has a regulated temperature, according to the specific thermal requirements of each assembly. Reflow ovens meant specifically for the soldering of SMT components may also be used for through-hole components by filling the holes with solder paste and inserting the component leads through the paste.
The goal of the reflow process is for the solder paste to reach the eutectic temperature at which the particular solder alloy undergoes a phase change to a liquid or molten state. At this specific temperature range, the molten alloy demonstrates properties of adhesion. Molten solder alloy behaves much as water, with properties of cohesion and adhesion. With sufficient flux, in the state of liquidus, molten solder alloys will exhibit a characteristic called “wetting.” Wetting is a property of the alloy when within its specific eutectic temperature range. Wetting is a necessary condition for the formation of solder joints that meet the criteria in the industry.
After the reflow process, a wafer is transferred to a buffer station through, for example, a wafer transportation assembly and a transfer robot. The wafer transportation assembly is a transportation mechanism configured to transport the wafer coming out of the reflow oven to a stopper and adjust the position (e.g., yaw, pitch, and roll) of the wafer to some extent, if necessary. However, due to the warpage of the wafer resulting from the reflow process, the wafer may not necessarily have the ideal position when it enters the wafer transportation assembly. Even though technologies, such as conveyors with differential speed, may be used, the results are sometimes unsatisfactory. For example, wafer scrap may occur, which is very costly. In some situations, the wafer may even be stuck in the wafer transportation assembly (sometimes referred to as “wafer congestion” or “wafer clogging”), and the manpower associated with fixing the stuck wafer and troubleshooting the problems is costly as well. Productivity is negatively impacted accordingly.
In accordance with some aspects of the disclosure, a wafer alignment assembly is provided. The wafer alignment assembly includes, among other elements, a first tapered wall, a second tapered wall, a first spring wall attached to an inner surface of the first tapered wall, a second spring wall attached to an inner surface of the first tapered wall, a first set of conveyor rollers, and a second set of conveyor rollers.
The first tapered wall and the second tapered wall are characterized by a tapered shape, which facilitates the smooth entry of the wafer assembly and reduces the possibility of collision of the wafer assembly against the pair of tapered walls. Additionally, a torque generated by the first spring wall and the second spring wall can rotate the wafer assembly and reset the position of the wafer assembly to the desired position. This can also prevent the wafer assembly from being stuck. Lastly, at least one of the first set of conveyor rollers and at least one of the second set of conveyor rollers are characterized by roller caps, which can result in momentarily vertical movement of the wafer assembly. The friction that prevents the wafer assembly from free movement horizontally is released momentarily as well, thereby facilitating the reset of the wafer assembly to the desired position. The function of the pair of spring walls can be further enhanced when the friction is released momentarily.
Consequently, the following advantages can be achieved. The possibility of wafer collision and wafer scrap is reduced. The wafer assembly is prevented from being stuck. Manpower in the semiconductor processing can be saved. The troubleshooting period, if there is any, can be shortened. Details of various aspects of the disclosure will be described below with reference to
Example Solder Reflow System
A wafer assembly 190, which includes a wafer 192 and a wafer frame 194, is transferred to the solder reflow oven 102 through an inlet 112 of the solder reflow over 102. After the reflow process, the wafer assembly 190 is transferred out of the solder reflow oven 102 through an outlet 114 of the solder reflow over 102. In some embodiments, the outlet 114 is aligned with the inlet of the wafer alignment assembly 104. While only one wafer 192 and one wafer frame 194 are shown in
In some implementations, the solder reflow oven 102 includes a reflow chamber, which has built-in heating/cooling plates. The wafer 192 is placed in close proximity to one of the built-in heating/cooling plates at a certain distance. The distance can prevent the formation of hot/cold zones that may be created when the wafer 192 is in contact with the built-in heating/cooling plate due to, for example, warpage. In other implementations, cooling is achieved using cooling gas flow.
In some implementations, the reflow chamber of the solder reflow oven 102 further includes a vacuum port and a gas port. In some examples, controlled heat can be achieved in vacuum using the vacuum port. In other examples, controlled heat can be achieved in a non-reactive gas environment using the gas port. Examples of the non-reactive gas include nitrogen, argon, helium, hydrogen, and the like.
The temperature profile (sometimes also referred to as the “thermal profile”) of the reflow process allows for the reflow of solder onto the adjoining surfaces to create permanent solder joints, without overheating and damaging the electrical components beyond their temperature tolerance. There are usually four stages (sometimes also referred to as “zones”), namely the preheat stage, the thermal soak stage, the reflow stage, and the cooling stage.
In the preheat stage, the wafer 192 is safely and consistently heated to a soak temperature. In addition, the preheat stage also provides an opportunity for volatile solvents in the solder paste to outgas. The thermal soak stage is typically an exposure (e.g., 60 to 120 seconds) for the removal of solder paste volatiles and the activation of the fluxes, where the flux components begin oxide reduction on component leads and pads. At the end of the thermal soak stage, a thermal equilibrium of the entire wafer 192 is desired before the reflow stage.
In the reflow stage, the peak temperature is reached. A common peak temperature is 20-40° C. above liquidus. The peak temperature is restricted by the components on the wafer 192 that have the lowest tolerance for high temperatures (i.e., the components most susceptible to thermal damage). Conversely, a temperature that is not high enough may prevent the solder paste from reflowing adequately.
In the cooling stage, the wafer 192 is gradually cooled, and the solder joints are solidified. Proper cooling inhibits excess intermetallic formation or thermal shock to the components. Typical temperatures in the cooling zone range from 30-100° C. In some embodiments, a relatively fast cooling rate is chosen to create a fine grain structure that is most mechanically sound.
As mentioned above, the wafer assembly 190 is transferred out of the solder reflow over 102, through the outlet 114 of the solder reflow over 102, to the wafer alignment assembly 104. The wafer assembly 190 is conveyed or transported from one end (i.e., the proximate end) to another end (i.e., the distant end) of the wafer alignment assembly 104. As will be explained in detail below with reference to
After the wafer assembly 190 is conveyed to the distant end, the transfer robot 106 transfers the wafer assembly 190 to the buffer station 108. In some implementations, the transfer robot 106 includes one or more rods connected end to end between a motor and a holding member by one or more bearings. The motor is configured to vertically, horizontally, and/or rotationally move the holding member along the bearings. In one embodiment, the holding member includes one or more blades, and each of the one or more blades includes a pair of laterally spaced fingers typically configured to support the wafer assembly 190.
The buffer station 108 is used as a buffer for balancing the process flow. When a wafer assembly 190 is conveyed to the distant end of the wafer alignment assembly 104, it cannot stay there for a long time because the solder reflow over keeps working and the next wafer assembly might arrive at the same place soon. If the wafer assembly 190 is not transferred to another place, a collision between the wafer assembly 190 and the next wafer assembly will occur. Therefore, the buffer station 108 serves as a buffer to prevent wafer assembly collision. On the other hand, the buffer station 108 can also regulate (i.e., increase or decrease) the temperature according to the process requirements.
Example Wafer Alignment Assembly
The wafer assembly 190 enters, in the first horizontal direction (i.e., the X-direction shown in
In the example shown in
The elongated segment 222a has a length W1 in the X-direction. As shown in
In some embodiments, the tapered walls 202a and 202b are made of stainless steel. In other embodiments, the tapered walls 202a and 202b are made of anodized aluminum. Anodizing is an electrochemical process that converts the metal surface into a durable, corrosion-resistant, and anodic oxide finish. It should be understood that these materials are exemplary rather than limiting, and the tapered walls 202a and 202b can be made of other suitable materials as needed in other embodiments.
The pair of spring walls 204a and 204b are attached to the inner surfaces of the pair of tapered walls 202a and 202b, respectively. The pair of spring walls 204a and 204b are operable to adjust the position of the wafer assembly 190 if the position of the wafer assembly 190 deviates from its desired position due to, for example, the warpage of the wafer 192, the torque applied to the wafer assembly 190, and the like. The detachable spring walls 204a and 204b make it easier to upgrade existing platforms in a cost-effective manner.
In the example shown in
The movable wall 234a is an elongated wall extending in the X-direction. The movable wall 234a is parallel to the fixed wall 232a in a free state (i.e., when no force is applied to the movable wall 234a). The movable wall 234a can move with respect to the fixed wall 232a.
The adjustable connection mechanisms 236a-1, 236a-2, and 236a-3 are distributed in the X-direction. The adjustable connection mechanisms 236a-1, 236a-2, and 236a-3 extend substantially in a second horizontal direction (i.e., the Y-direction shown in
Each of the adjustable connection mechanisms 236a-1, 236a-2, and 236a-3 can adjust its length in the Y-direction, thereby enabling the movement of the movable wall 234a. In one implementation, each of the adjustable connection mechanisms 236a-1, 236a-2, and 236a-3 includes an extensible pin structure and a spring inside the extensible pin structure, as shown in
While each of the adjustable connection mechanisms 236a-1, 236a-2, and 236a-3 is implemented as having an extensible pin structure and a spring inside it in the example described above, it should be understood that the adjustable connection mechanisms 236a-1, 236a-2, and 236a-3 can be implemented in other suitable manners.
Also, while three adjustable connection mechanisms 236a-1, 236a-2, and 236a-3 are shown in
The fixed wall 232a and the movable wall 234a both have a length W2 in the X-direction. In one embodiment, the length W2 is equal to the length W1. In other words, the length W2 is the same as the length W1 of the elongated segment 222a shown in
In some embodiments, the distance Y between the fixed wall 232a and the movable wall 234a is larger than 2 mm and smaller than 5 mm. In other embodiments, the distance Y between the fixed wall 232a and the movable wall 234a is larger than 3 mm and smaller than 4 mm.
As shown in
In one embodiment, the distance between the movable wall 234a and the movable wall 234b (when both are in their resting positions) is adjustable. In one example, the distance between the movable wall 234a and the movable wall 234b (when both are in their resting positions) is adjusted to be substantially the same as the critical dimension of the wafer assembly 190 in the Y-direction shown in
Referring back to
In the example shown in
In some embodiments, the roller cap 242 is a separate and detachable piece attached to or mounted on the conveyor roller 206a-2. The detachable roller cap 242 makes it easier to upgrade existing conveyor rollers in a cost-effective manner. In other embodiments, the roller cap 242 and the conveyor roller 206a-2 are fabricated as on-piece using, for example, molding. The one-piece design can enhance the strength and reliability of the roller cap 242.
In some embodiments, the roller cap 242 is made of stainless steel. In other embodiments, the roller cap 242 is made of aluminum. It should be understood that these materials are exemplary rather than limiting, and the roller cap 242 can be made of other suitable materials as needed in other embodiments.
In the example shown in
In contrast, the presence of the roller cap 242 on the conveyor roller 206a-2 can raise the wafer assembly 190 to some extent, as shown in
Because of the vertical movement of the wafer assembly 190, the normal force between the wafer assembly 190 and the conveyor roller 206a-2 can be released momentarily. As a result, the friction that prevents the wafer assembly 190 from free movement horizontally is released momentarily as well, thereby facilitating the reset of the wafer assembly 190 to the desired position. The function of the pair of spring walls 204a and 204b can be further enhanced when the friction is released momentarily.
As the conveyor roller 206a-2 rotates, the roller cap 242 encounters the wafer assembly 190 periodically, assuming that the rotation speed of the conveyor roller 206a-2 is constant. Accordingly, the friction is released momentarily multiple times in some embodiments.
Although only one roller cap 242 is used in the example shown in
Also, it should be understood that not all the conveyor rollers 206a and 206b are characterized by at least one roller cap 242. In the example shown in
In other embodiments, more than three of the conveyor rollers 206a are characterized by at least one roller cap 242; more than three of the conveyor rollers 206b are characterized by at least one roller cap 242.
In the configuration shown in
One of ordinary skill in the art would recognize many variations, modifications, and alternatives in view of
The wafer stopper 210 is located at the distant end 294. The wafer stopper 210 is configured to stop the wafer assembly 190, and the wafer assembly 190 is subsequently transferred, by the transfer robot 106, to the buffer station 108. In some embodiments, the wafer stopper 210 further includes some positioning sensors (e.g., laser sensors) that can determine whether the wafer assembly 190 reaches a certain location.
Example Method for Processing a Wafer Assembly
At operation 1202, a reflow process is performed on a wafer assembly (e.g., the wafer assembly 190 shown in
At operation 1204, the wafer assembly is conveyed, by a wafer alignment assembly (e.g., the wafer alignment assembly 104 shown in
At operation 1206, the wafer assembly is transferred to a buffer station (e.g., the buffer station 108 shown in
Consequently, the following advantages can be achieved. The possibility of wafer collision and wafer scrap is reduced. The wafer assembly is prevented from being stuck. Manpower in the semiconductor processing can be saved. The troubleshooting period, if there is any, can be shortened.
In one example, the wafer scrap can be reduced from 1.5 pieces per month to zero; the manpower needed can be reduced by 80% (from 0.5 units to 0.1 units); the troubleshooting period can be reduced from 3.2 hours per day to zero; the platform available time can be increased by 6%.
In accordance with some aspects of the disclosure, a wafer alignment assembly is provided. The wafer alignment assembly includes: a first tapered wall extending in a first horizontal direction; a first spring wall attached to an inner surface of the first tapered wall; a first set of conveyor rollers configured to rotate; a second tapered wall extending in the first horizontal direction, wherein the first tapered wall and the second tapered wall are characterized by a tapered shape that facilitates entry of a wafer assembly; a second spring wall attached to an inner surface of the first tapered wall; and a second set of conveyor rollers configured to rotate.
In accordance with some aspects of the disclosure, a solder reflow system is provided. The solder reflow system includes: a solder reflow oven configured to perform a reflow process; a buffer station configured to accommodate wafer assemblies after the reflow process; and a wafer alignment assembly located between the solder reflow oven and the buffer station. The wafer alignment assembly includes: a first tapered wall extending in a first horizontal direction; a first spring wall attached to an inner surface of the first tapered wall; a first set of conveyor rollers configured to rotate; a second tapered wall extending in the first horizontal direction, wherein the first tapered wall and the second tapered wall are characterized by a tapered shape that facilitates entry of a wafer assembly; a second spring wall attached to an inner surface of the first tapered wall; and a second set of conveyor rollers configured to rotate.
In accordance with some aspects of the disclosure, a method is provided. The method includes the following steps: performing a reflow process on a wafer assembly; and conveying the wafer assembly, by a wafer alignment assembly, from a proximate end to a distant end of the wafer alignment assembly. The wafer alignment assembly includes: a first tapered wall extending in a first horizontal direction; a first spring wall attached to an inner surface of the first tapered wall; a first set of conveyor rollers configured to rotate; a second tapered wall extending in the first horizontal direction, wherein the first tapered wall and the second tapered wall are characterized by a tapered shape that facilitates entry of the wafer assembly; a second spring wall attached to an inner surface of the first tapered wall; and a second set of conveyor rollers configured to rotate.
The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.
