Method for enabling floor height to reach standard height by controlling module counterweight

Abstract

The invention relates to a method for enabling floor height to reach a standard height by controlling module counterweight. The method comprises the following steps of: determining a material, a size and a standard reflow curve of a required solder ball; preparing a substrate, a clamp and a counterweight copper block; reflowing after welding a solder ball on the substrate, and measuring the height of the solder ball after reflowing; reflowing again after adding a substrate and a counterweight copper block, and measuring the height of the solder ball after reflowing again; calculating the weight borne by a single solder ball; and calculating the standard interlayer height. The method has the advantages that interlayer height control of the multi-layer module is achieved through the clamp and the balance weight, interconnection reliability of interlayer solder balls is guaranteed, and the defects that the number of backflow times is increased and the height cannot be finely adjusted when copper core balls are planted are overcome. The method is simple in implementation process, high in control precision and easy to operate.

Description

Technical Field

[0001] The invention relates to a method for making a layer height reach a standard height by controlling module counterweight, and belongs to the technical field of electronic packaging technology. Background Art

[0002] With the development of system-level packaging, module products with multi-layer stacked structures are widely used in the internal integration of electronic devices. The circuit connection between the upper and lower layers of the stacked structure is mainly achieved by solder balls. The shape of the solder balls after reflow will affect the connection performance, signal transmission and structural support of the upper and lower layers. The shape of the solder balls is affected by the weight above them, such as the upper substrate, the upper ball grid array (BGA) layer and components. In addition, in order to reduce the deformation of the substrate during the module reflow process, the pressure above the module will also increase. At present, copper core balls are mostly used for the height limit between layers. The implantation of copper core balls increases the number of reflows, and the preparation of copper core balls is complicated. The prepared copper core balls have problems such as poor shape regularity, poor roundness, and irregular surface. If the pressure above is too large, the copper core balls will squeeze the substrate. Therefore, in order to ensure the interconnection reliability between the layers of the module, a method that can pre-control the height of the solder balls between the layers is needed. Summary of the invention

[0003] The present invention proposes a method for achieving a standard layer height by controlling the module weight, and aims to address the defects of the prior art. For multi-layer module products, the solder balls can collapse to the required height after reflow by changing the weight above the solder ball layer.

[0004] The technical solution of the present invention is a method for making the floor height reach the standard height by controlling the module counterweight, comprising the following steps: (1) Determine the required solder ball material, size and standard reflow curve; (2) Prepare the substrate, fixture and counterweight copper block, and measure the weight of the substrate, recorded as G0; (3) After soldering the solder ball on the substrate, reflow is performed and the height of the solder ball after reflow is measured, which is recorded as H0; (4) Add another substrate on top of the substrate in step (3), add a counterweight copper block on the substrate and reflow again, and measure the height of the solder ball after reflow again, which is recorded as H1; (5) Calculate the weight borne by a single solder ball; (6) Calculate the standard inter-story height.

[0005] In the step (2), the pads on the substrate are distributed in a matrix structure, and the substrate is cleaned by a vapor phase cleaning machine and then weighed, with the weight recorded as G0; the size of the counterweight copper block is consistent with that of the substrate, and the weight of the counterweight copper block is changed by changing the thickness.

[0006] In the step (3), the substrate is coated with flux and then the balls are implanted, which are then placed in a reflow furnace for reflow. The solder balls on each pad on the substrate are wetted, and the height of the solder balls after reflow is measured using an ultra-depth of field optical microscope, which is recorded as H0.

[0007] In the step (4), the substrate in step (3) is placed in a fixture, and the vertical heights of the layers are aligned by means of a limit frame on the fixture. After alignment, the limit frame is removed, and the substrate is placed in a reflow furnace for reflow. The height of the solder ball after reflow is measured using an ultra-depth of field optical microscope, which is recorded as H1.

[0008] In step (5), the weight of the counterweight copper block when H1=0.6H0 is recorded as G1, and the weight G borne by a single solder ball is calculated as follows: G=(G0+G1) / X, where X is the number of solder balls.

[0009] Beneficial effects of the present invention: 1) The present invention realizes the interlayer height control of the multi-layer module through the clamp and the counterweight, ensures the interconnection reliability of the interlayer solder balls, and avoids the defects of increasing the number of reflow times and the height cannot be fine-tuned due to the implantation of copper core balls.

[0010] 2) The present invention has a simple implementation process, high control accuracy and is easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Attached Figure 1 It is a flow chart of a method for controlling the height of solder balls between module layers.

[0012] Attached Figure 2 It is a schematic diagram of the fixture structure.

[0013] Attached Figure 3 It is a structural schematic diagram of the reflow process of adding copper counterweight blocks.

[0014] Attached Figure 4 Schematic diagram of the height of solder balls after reflow with different weights in the embodiment. DETAILED DESCRIPTION

[0015] The technical solution of the present invention is further explained below in conjunction with the accompanying drawings.

[0016] As attached Figure 2 As shown, the limit frame and the fixture bottom plate are fixed with screws, the fixture is made of stainless steel, and the limit frame height can be adjusted according to the module height. The use process is to first fix one of the limit frames on the fixture bottom plate, place the substrate in the frame to align the limit frame, and then fix the other limit frame to completely lock the substrate.

[0017] As attached Figure 3As shown in the figure, the schematic diagram of the alignment process of each layer before reflow, from top to bottom in the figure are the counterweight copper block, substrate, solder ball layer, substrate, and fixture. Before the multi-layer structure is reflowed, one of the limit frames is also fixed on the bottom plate of the fixture, and the substrate is placed in the frame. The substrate above the solder ball layer is coated with flux and placed, and finally the counterweight copper block is placed. Another limit frame is used to align the vertical height of each layer of the substrate and the copper block. After removing the limit frame, it is placed in the reflow furnace for reflow.

[0018] Example 1

[0019] As attached Figure 1 As shown, a method for making the floor height reach a standard height by controlling the module counterweight comprises the following steps: (1) Determine the required solder ball material and size. The solder ball is a SAC305 solder ball with a diameter of 300 μm.

[0020] (2) Determine the standard reflow curve for solder ball reflow. The SAC305 solder ball reflow curve is as follows: the temperature in the heating zone is raised from room temperature to 150°C, and the time is set at 60-90s; the temperature in the constant temperature zone is gently raised from 150°C to 200°C, and the time is set at 60-120s; the temperature in the reflow zone is raised to 240°C, and the time is set at 30-70s; the temperature in the cooling zone is lowered to 170°C, and the cooling rate is greater than 2.5°C / s. The solder ball reflow process is carried out in the same reflow furnace.

[0021] (3) Prepare the substrate. The pads on the substrate are distributed in a matrix structure. They can be distributed in 10*10 or 20*20 patterns. A 10*10 pad has 100 solder balls, and a 20*20 pad has 400 solder balls. Use a vapor phase cleaning machine to clean the substrate and weigh it. The weight is recorded as G0. Prepare a counterweight copper block. The size of the copper block is consistent with that of the substrate. By changing the thickness, counterweight copper blocks of different weights can be obtained. The weight ranges from 1g to 20g.

[0022] (4) Prepare a fixture. The function of the fixture is to calibrate the multi-layer structure and ensure the alignment accuracy of each layer.

[0023] (5) Solder the solder balls on the substrate, apply flux to the substrate and then place the balls in a reflow oven to ensure that the solder balls on each pad are well wetted. Use an ultra-depth of field optical microscope to measure the height of the solder balls after reflow, which is recorded as the T0 state.

[0024] (6) Place the substrate in the T0 state into the fixture, add a layer of substrate on top, and add a counterweight copper block on the substrate. Use the limit frame on the fixture to align the vertical heights of each layer. After alignment, remove the limit frame and place it in the reflow furnace. After reflow, measure and record the height of the solder balls after reflow corresponding to the different weights of the copper blocks, and record it as the T1 state. The removal of the limit frame ensures that the solder balls are only affected by the weight drop from the top during the reflow process, eliminating the force on the side.

[0025] (7) According to the industry and IPC standards, the standard collapse height of the solder ball is approximately 60% of the solder ball diameter. Calculate the sum of the weight of the copper block G1 corresponding to the height reaching 60% of the solder ball diameter in the T1 state and the weight of the substrate itself G0, and divide it by the number of solder balls X to obtain the weight G borne by a single solder ball at this time. The formula is as follows: G = (G0 + G1) / X.

[0026] In actual production, for stacked modules, the number of solder balls used is known, and the value obtained by multiplying it by the weight borne by a single solder ball is used. The weight above the solder ball layer is adjusted according to the numerical result to obtain the standard interlayer height.

[0027] As attached Figure 4 As shown in the figure, the height measurement of SAC305 solder balls with a diameter of 300 microns after being weighed with different weights. 100 SAC305 solder balls with a diameter of 300 microns reach an approximate value of 180 microns, and the corresponding copper block weight in the figure is between 8-10g, plus the weight of the substrate 0.24g, it is calculated that the weight of a single solder ball at this time is 0.0924g.

[0028] G0=0.24g, G1=9g, X=100, then G=(0.24+9) / 100=0.094g.

[0029] After that, once the number of solder balls is known, the weight required to achieve the desired layer height can be calculated.

Claims

1. A method for achieving a standard height of a floor by controlling the weight of a module, characterized in that The following steps are involved: Determine the required solder ball material, size and its standard reflow profile; Prepare the substrate, fixture and counterweight copper block, measure the weight of the substrate, and record it as G0; After soldering the solder ball on the substrate, reflow is performed and the height of the solder ball after reflow is measured and recorded as H0; In step (3), another substrate is added on top of the substrate, a counterweight copper block is added to the substrate and reflow is performed again, and the height of the solder ball after reflow is measured and recorded as H1; Calculate the weight borne by a single solder ball; Calculate the standard floor height.

2. A method for achieving a standard height of a floor by controlling the weight of a module according to claim 1, characterized in that In the step (2), the pads on the substrate are distributed in a matrix structure, and the substrate is cleaned by a vapor phase cleaning machine and then weighed, with the weight recorded as G0; the size of the counterweight copper block is consistent with that of the substrate, and the weight of the counterweight copper block is changed by changing the thickness.

3. The method of making the floor height reach the standard height by controlling the module counterweight according to claim 1, characterized in that In the step (3), the substrate is coated with flux and then the balls are implanted, which are then placed in a reflow furnace for reflow. The solder balls on each pad on the substrate are wetted, and the height of the solder balls after reflow is measured using an ultra-depth of field optical microscope, which is recorded as H0.

4. The method of making the floor height reach the standard height by controlling the module counterweight according to claim 1, characterized in that In step (4), the substrate in step (3) is placed in a fixture, and the vertical heights of the layers are aligned by the limit frames on the fixture. After alignment, the limit frames are removed and the substrate is placed in a reflow furnace for reflow. The height of the solder ball after reflow is measured using an ultra-depth of field optical microscope and recorded as H1.

5. The method of making the floor height reach the standard height by controlling the module counterweight according to claim 1, characterized in that In step (5), the weight of the counterweight copper block when H1=0.6H0 is recorded as G1, and the weight G borne by a single solder ball is calculated as follows: G=(G0+G1) / X, where X is the number of solder balls.

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