A method for controlling the temperature of a BGA device using a fixture during reflow

Abstract

The present application relates to a kind of method for controlling BGA device temperature using tool in reflow soldering process, belong to integrated circuit manufacturing technical field.The present application selects tool manufacturing material, tool thickness L and air gap thickness d according to the size of BGA device, expected cooling effect;Before reflow soldering, tool covers BGA device body and solder point area;Tool is semi-enclosed structure, when tool covers BGA device body and solder point area, with the printed circuit board below and form fully enclosed structure.The present application gives the specific accurate calculation and control method using tool cooling, realizes accurate cooling within 20 DEG C to BGA device body by the thermal resistance design of tool, avoids device overheating.

Description

Technical Field

[0001] This invention belongs to the field of integrated circuit manufacturing technology, specifically relating to a method for controlling the temperature of BGA devices using tooling during reflow soldering. Background Technology

[0002] As electronic products become more multifunctional and high-density, the variety of chips designed on printed circuit board (PCB) assemblies is increasing, leading to conflicting soldering requirements from some component manufacturers. In the reflow soldering process of integrated circuits, the soldering quality of BGA devices directly affects product reliability. In traditional reflow soldering processes, BGA devices suffer from poor overall heating uniformity, especially ceramic-packaged BGA devices. Due to their large heat capacity, this can easily lead to excessively high device temperatures and insufficient solder joint temperatures, thus affecting soldering quality. Current technologies typically use methods such as adding heat sinks or adjusting the oven temperature profile to control temperature, but these methods have the following problems:

[0003] 1. Heat sinks increase manufacturing complexity and make precise temperature control difficult;

[0004] 2. Adjusting the furnace temperature profile can affect the welding quality of other components, making it difficult to achieve local temperature control.

[0005] Therefore, there is an urgent need for a tooling and design method that can precisely control the body temperature of BGA devices while ensuring that the solder joint temperature meets the requirements for reflow soldering. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] The technical problem to be solved by this invention is how to provide a method for controlling the temperature of BGA devices using tooling during reflow soldering, so as to solve the problems that heat sinks increase process complexity and make it difficult to control the temperature accurately; and that adjusting the furnace temperature profile will affect the soldering quality of other devices and make it difficult to achieve local temperature control.

[0008] (II) Technical Solution

[0009] To address the aforementioned technical problems, this invention proposes a method for controlling the temperature of BGA devices using tooling during reflow soldering. This method includes the following steps:

[0010] S1. Select the tooling material, tooling thickness L, and air gap thickness d based on the size of the BGA device and the expected cooling effect.

[0011] S2. Before reflow soldering, cover the BGA device body and solder joint area with the fixture; the fixture has a semi-enclosed structure. After the fixture covers the BGA device body and solder joint area, it forms a fully enclosed structure with the printed circuit board below.

[0012] S3. Perform the reflow soldering process.

[0013] (III) Beneficial Effects

[0014] This invention proposes a method for controlling the temperature of BGA devices using tooling during reflow soldering. The advantages of this invention are:

[0015] 1. This invention provides a precise calculation and control method for cooling using tooling. Through the thermal resistance design of the tooling, precise cooling of the BGA device body within 20°C can be achieved, avoiding overheating of the device.

[0016] 2. This invention adopts a fully enclosed design to ensure that the temperature of the welding point area meets the welding requirements, and that the welding is uniform in all directions, thereby improving the welding quality;

[0017] 3. The tooling structure is simple, easy to manufacture and install, and suitable for large-scale production. Attached Figure Description

[0018] Figure 1 The heat conduction sequence before and after using the tooling of the present invention; (a) before using the tooling; (b) after using the tooling;

[0019] Figure 2 Temperature profiles before and after using the tooling;

[0020] Figure 3 This is a schematic diagram of the tooling of the present invention. Detailed Implementation

[0021] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0022] This invention relates to the field of integrated circuit manufacturing technology, specifically to a tooling and its design method for temperature control of risky devices during reflow soldering of high-density printed circuit board assemblies, and is particularly applicable to the soldering process of ceramic packaged BGA devices.

[0023] The purpose of this invention is to provide a method for controlling the temperature of BGA devices during reflow soldering using a tooling system. This invention achieves precise cooling of the BGA device body through a fully enclosed tooling design and its thermal resistance calculation model, while ensuring that the solder joint temperature meets soldering requirements. This invention has advantages such as simple structure, ease of manufacture, and wide applicability, and can significantly improve the soldering quality of BGA devices. This invention achieves precise cooling of the BGA device body through the thermal resistance design of the tooling, while ensuring that the solder joint temperature meets soldering requirements.

[0024] 1. This invention provides a method for controlling the temperature of BGA devices using tooling during reflow soldering, the method comprising:

[0025] S1. Select the tooling material, tooling thickness L, and air gap thickness d based on the size of the BGA device and the expected cooling effect.

[0026] The temperature that can be cooled can reach 0-20℃.

[0027] Specifically, based on the thermal characteristics of BGA devices, the expected cooling effect is determined, and then the target value of the thermal resistance on the tooling side is determined; by adjusting the tooling material, tooling thickness L, and air gap thickness d, the precise control of the thermal resistance on the tooling side is achieved.

[0028] S2. Before reflow soldering, cover the BGA device body and solder joint area with the fixture; the fixture has a semi-enclosed structure. After the fixture covers the BGA device body and solder joint area, it forms a fully enclosed structure with the printed circuit board below.

[0029] When using the device, the heat insulation fixture is placed downwards on the BGA device body and solder joint area that require heat insulation, without contacting the BGA device body.

[0030] The tooling material is synthetic stone or polyimide, which has low thermal conductivity.

[0031] An air gap is provided between the fixture and the surface of the BGA device to further increase thermal resistance. Due to the limited space of the high-density printed circuit board, the distance between the BGA device and the fixture is the same and fixed on all sides. The distance between the upper surface of the BGA device and the fixture, i.e. the thickness d of the air gap, can be adjusted.

[0032] S3. Perform the reflow soldering process.

[0033] 2. Thermal resistance design method

[0034] - Thermal resistance R of components during reflow soldering without tooling 原热阻 R is the convective heat transfer resistance of the device. 器件对流 Thermal resistance R on the printed circuit board side PCB侧 The parallel value is calculated using the following formula:

[0035]

[0036] in:

[0037]

[0038] h1 is the convective heat transfer coefficient in the reflux furnace, A 器件表面积 k is the surface area of ​​the device. PCB For the thermal conductivity of printed circuit boards (typically 0.2–0.4 W / (m·K)), A 印制板面积 L is the bottom surface area of ​​the printed circuit board. PCB This refers to the thickness of the printed circuit board.

[0039] When using a fixture, the thermal resistance on the PCB side is the same as when no fixture is used. The heat transfer on the component side changes from direct convection heat transfer from hot air to the component to convection heat transfer from hot air to the fixture. Heat transfer and radiation occur between the fixture, the air, and the component. The thermal resistance on the fixture side consists of the reflow soldering convection heat transfer resistance to the fixture, the material thermal resistance, the air gap thermal resistance, and the natural convection heat transfer from the component. The calculation formula is:

[0040] R 工装侧 =R 工装对流 +R material +R air +R 自然换热

[0041] in:

[0042]

[0043] L is the tooling thickness, k material d is the thermal conductivity of the tooling material, d is the air gap thickness, and k is the thermal conductivity of the tooling material. air Let A be the thermal conductivity of air, and A be the area covered by the tooling. 工装表面积 h1 is the surface area of ​​the tooling, and h2 is the natural convection heat transfer coefficient.

[0044] By adjusting the tooling material, tooling thickness L, and air gap thickness d, the thermal resistance of the tooling can be controlled to achieve precise cooling of the BGA device body.

[0045] 3. Calculation of cooling effect

[0046] -Total thermal resistance R when using tooling for reflow soldering total For tooling thermal resistance R 工装侧 With printed circuit board thermal resistance R PCB侧 The parallel value is calculated using the following formula:

[0047]

[0048] The cooling effect is represented by the percentage decrease in temperature when using a fixture for reflow soldering compared to reflow soldering without a fixture. The formula for calculating the percentage decrease in temperature is as follows:

[0049]

[0050] Example 1:

[0051] The present invention will be described in detail below with reference to the embodiments:

[0052] 1. Tooling Design

[0053] - The tooling material is synthetic stone, with a thermal conductivity of kJ / k. material =0.25W / (m·K);

[0054] - Tooling thickness L = 0.0025m, air gap thickness d = 0.0005mm;

[0055] - Tooling coverage area A = 0.000625m 2 Here, the surface area of ​​the tooling and the surface area of ​​the device are approximated as the area covered by the tooling;

[0056] - The forced convection heat transfer coefficient of the reflux furnace is approximately h1≈43W / (m·K).

[0057] - The natural convection heat transfer coefficient h2≈10W / (m·K)

[0058] - Thermal conductivity of printed circuit board (k) PCB = 0.3 W / (m·K)

[0059] -Printed circuit board thickness L PCB =0.002mm

[0060] - Printed board area A PCB =0.03m 2 .

[0061] 2. Thermal resistance calculation

[0062] - Tooling convection heat transfer thermal resistance:

[0063]

[0064] - Material thermal resistance:

[0065]

[0066] -Air gap thermal resistance:

[0067]

[0068] -Thermal resistance of the device due to natural convection heat transfer:

[0069]

[0070] -Total thermal resistance on the tooling side:

[0071] R 工装侧 =R 对流换热 +R material +R air +R 自然换热 =237.45K / W

[0072] -Convection heat transfer thermal resistance of the original components:

[0073]

[0074] - Printed circuit board convective heat transfer thermal resistance:

[0075]

[0076] -Printed circuit board thermal resistance:

[0077]

[0078] 3. Cooling effect

[0079] -Original thermal resistance:

[0080]

[0081] -Total thermal resistance:

[0082]

[0083] -Percentage of temperature reduction:

[0084]

[0085] The beneficial effects of this invention are:

[0086] 1. This invention provides a precise calculation and control method for cooling using tooling. Through the thermal resistance design of the tooling, precise cooling of the BGA device body within 20°C can be achieved, avoiding overheating of the device.

[0087] 2. This invention adopts a fully enclosed design to ensure that the temperature of the welding point area meets the welding requirements, and that the welding is uniform in all directions, thereby improving the welding quality;

[0088] 3. The tooling structure is simple, easy to manufacture and install, and suitable for large-scale production.

[0089] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for controlling the temperature of BGA devices using tooling during reflow soldering, characterized in that, The method includes the following steps: S1. Select the tooling material and thickness based on the size of the BGA device and the expected cooling effect. L and air gap thickness d ; S2. Before reflow soldering, cover the BGA device body and solder joint area with the fixture; the fixture has a semi-enclosed structure. After the fixture covers the BGA device body and solder joint area, it forms a fully enclosed structure with the printed circuit board below. S3. Perform the reflow soldering process; in, In step S1, the cooling effect is represented by the percentage decrease in temperature when using a tooling for reflow soldering compared to when not using a tooling for reflow soldering. The formula for calculating the percentage decrease in temperature is as follows: in, The thermal resistance of the device during reflow soldering without tooling. The total thermal resistance when using tooling for reflow soldering; The total thermal resistance during reflow soldering using tooling For tooling thermal resistance Thermal resistance of printed circuit board The parallel value is calculated using the following formula: When using a fixture, the thermal resistance on the PCB side is the same as when the fixture is not used. The heat transfer on the device side changes from direct convection heat transfer from hot air to the device to convection heat transfer from hot air to the fixture. The fixture, air, and device are involved in heat transfer and thermal radiation. The thermal resistance on the fixture side consists of the heat transfer resistance from reflow soldering to the fixture, the material thermal resistance, the air gap thermal resistance, and the natural convection heat transfer of the device. in: L For tooling thickness, For the thermal conductivity of tooling materials, d For air gap thickness, For the thermal conductivity of air, A For the area covered by the tooling, The surface area of ​​the tooling. The coefficient of heat transfer is the natural convection heat transfer coefficient. The convective heat transfer resistance of the device Thermal resistance on the printed circuit board side The parallel value is calculated using the following formula: in: The convective heat transfer coefficient in the reflux furnace. The surface area of ​​the device. For printed circuit board thermal conductivity, This refers to the bottom surface area of ​​the printed circuit board. This refers to the thickness of the printed circuit board.

2. The method for controlling the temperature of BGA devices using tooling during reflow soldering as described in claim 1, characterized in that, In step S1, the expected cooling effect is determined based on the thermal characteristics of the BGA device, and then the target value of the thermal resistance on the tooling side is determined; by adjusting the tooling material, tooling thickness L and air gap thickness d, the precise control of the thermal resistance on the tooling side is achieved.

3. The method for controlling the temperature of BGA devices using tooling during reflow soldering as described in claim 1, characterized in that, In step S2, the heat insulation fixture is placed downwards on the BGA device body and solder joint area that require heat insulation, without contacting the BGA device body.

4. The method for controlling the temperature of BGA devices using tooling during reflow soldering as described in claim 1, characterized in that, In S2, the tooling material is synthetic stone or polyimide.

5. The method for controlling the temperature of BGA devices using tooling during reflow soldering as described in claim 1, characterized in that, In S2, an air gap is provided between the tooling and the surface of the BGA device to increase thermal resistance. The distance between the BGA device and the tooling is the same and fixed around the perimeter. The distance between the upper surface of the BGA device and the tooling, i.e., the thickness d of the air gap, can be adjusted.

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