Manufacturing method for solving small plate thickness of BGA (Ball Grid Array) position of server

Abstract

The invention discloses a manufacturing method for solving the problem of small board thickness of a BGA position of a server, and relates to the technical field of server board processing, comprising an inner layer manufacturing process and an outer layer manufacturing process; the inner layer manufacturing process comprises the following steps of: a, sequentially performing inner layer pattern transfer and inner layer etching after cutting; b, after AOI detection, resin printing is carried out at the BGA position of the selected GND layer; c, pre-baking the resin at the temperature of a press; d, after the brownification treatment is completed, a pressing process is carried out; the outer layer manufacturing process comprises the steps that a, drilling, electroplating and back drilling are conducted after pressing is conducted; and b, carrying out resin hole plugging and then carrying out secondary electroplating to form the POFV structure. According to the method, the compensation model is established by pressing the FA verification plate, and the resin printing thickness is dynamically adjusted, so that the problem of non-uniform plate thickness in the BGA area is solved, the missing solder phenomenon of a printed chip is avoided, and meanwhile, the signal delay and abnormal heat dissipation of a product caused by copper laying are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of server board processing, and in particular to a manufacturing method for solving the problem of small thickness of a server BGA position board. Background Art

[0002] In the early 21st century, the rise of big data and cloud computing technologies led to exponential growth in data volumes, necessitating greater computing power and storage capacity for servers. In recent years, the rapid development of AI and ML technologies has placed even higher demands on server computing performance, driving the design and manufacture of high-performance server PCBs. However, server boards are relatively thin, and their solder pads are recessed relative to the rest of the board, hindering chip placement and prone to dry solder joints.

[0003] Currently, there is no specific control over the board thickness at the BGA location, and copper can be added at the beginning of the design to improve it. However, existing manufacturing solutions place copper in the signal layer, but excessive copper can lead to poor heat dissipation, increased parasitic capacitance, and signal delays. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for manufacturing a server BGA plate with a smaller thickness, so as to solve the above-mentioned technical deficiencies.

[0005] In order to achieve the above-mentioned object, the present invention provides the following technical solution: a manufacturing method for solving the problem of small thickness of the BGA plate at the server, comprising:

[0006] Inner layer production process and outer layer production process;

[0007] The inner layer production process includes:

[0008] a. After cutting, the inner layer pattern transfer and inner layer etching are carried out in sequence;

[0009] b. After passing AOI inspection, resin printing is performed at the selected BGA position on the GND layer. The number of resin printing layers is determined based on the core board stacking structure. The resin printing range is precisely limited to the BGA pad projection area, and the printing thickness is designed based on the board thickness difference value obtained from FA testing;

[0010] c. Use press temperature to pre-bake the resin;

[0011] d. After the browning process is completed, the pressing process begins;

[0012] The outer layer production process includes:

[0013] a. Drilling, electroplating and back drilling after pressing;

[0014] b. After implementing resin plugging, secondary electroplating is performed to form a POFV structure;

[0015] c. After the outer layer pattern is completed, solder mask processing, character printing and surface treatment are carried out in sequence;

[0016] d. Finally, the products are put into storage after molding, electrical testing and quality inspection.

[0017] The resin printing thickness is dynamically adjusted through FA testing to solve the problem of small board thickness caused by uneven pressing in the BGA area, and the thickness compensation accuracy is improved to ±5μm.

[0018] Preferably, in step b of the inner layer production process, a pressed FA verification plate is made in advance, and the actual plate thickness difference value ΔH is measured using the pressed FA verification plate to establish a compensation model:

[0019] ΔH = H reference - (H measured + δ), where δ is the process allowance of 0.05-0.15mm;

[0020] The measured deviation is corrected by the process allowance δ to avoid excessive plate thickness caused by overcompensation.

[0021] Preferably, in step b of the inner layer production process, the resin printing covers at least two adjacent GND layers, and the thickness of a single layer printing is controlled at 5-15 μm;

[0022] Resin printing covers adjacent GND layers to balance interlayer stress and reduce warpage.

[0023] Preferably, in step b of the inner layer production process, the resin printing adopts screen printing, the screen mesh number is 200-400 mesh, and the printing accuracy is ±0.02mm;

[0024] The fine screen ensures that the resin accurately covers the BGA projection area, reducing position deviation.

[0025] Preferably, in step c of the inner layer production process, resin baking adopts segmented temperature control:

[0026] The first stage is 80-100℃ / 30-45min to eliminate solvent volatilization;

[0027] The second stage is 120-135℃ / 60-90min to complete the resin cross-linking and curing;

[0028] The staged heating avoids the formation of skin on the resin surface, and the internal curing is complete. The slow heating reduces the thermal expansion difference between the core board and the resin interface, thereby improving the interface bonding strength.

[0029] Preferably, in step a of the outer layer production process, during back drilling, the drilling depth tolerance is controlled within ±0.075 mm, and the residual column height is ≤0.25 mm;

[0030] Residual column height control reduces signal reflection and lowers insertion loss.

[0031] Preferably, in step b of the outer layer production process, the resin plug holes are filled in two steps:

[0032] Step 1: Vacuum plugging, vacuum degree -0.08MPa to -0.1MPa, to eliminate bubbles;

[0033] Step 2: Pressure filling, pressure 0.3-0.5MPa, to ensure the density of the hole;

[0034] The synergistic effect of vacuum and pressure results in a high resin filling rate in the hole. Step-by-step control prevents resin overflow and improves the flatness of the hole mouth.

[0035] Preferably, in step b of the outer layer production process, the thickness of the secondary electroplated copper is controlled at 15-25 μm, the hole copper thickness is ≥25 μm, and the thick hole copper ensures the mechanical strength of the hole wall.

[0036] Preferably, in step c of the outer layer manufacturing process, the surface treatment adopts an immersion gold process, the nickel layer thickness is 3-5 μm, and the gold layer thickness is 0.05-0.1 μm, and the immersion gold layer provides a stable welding surface.

[0037] Preferably, the resin material is epoxy-modified acrylic resin, and the CTE after curing is ≤50ppm / °C. The low CTE resin reduces thermal cycle stress and reduces the risk of delamination.

[0038] In the above technical solution, the technical effects and advantages provided by the present invention are:

[0039] 1. It can solve the problem of thin board thickness at BGA position and avoid the phenomenon of empty soldering when punching chips;

[0040] 2. It can improve product signal delay and abnormal heat dissipation caused by copper plating. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments described in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0042] Figure 1 This is a schematic diagram of the inner layer manufacturing process of the present invention;

[0043] Figure 2 Schematic diagram of the outer layer production process of the present invention. DETAILED DESCRIPTION

[0044] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0045] The present invention provides Figures 1 to 2 A method for solving the problem of small board thickness at the server BGA position is shown, including:

[0046] Inner layer production process and outer layer production process;

[0047] The inner layer production process includes:

[0048] a. After cutting, the inner layer pattern transfer and inner layer etching are carried out in sequence;

[0049] b. After passing AOI inspection, resin printing is performed at the selected BGA position on the GND layer. The number of resin printing layers is determined based on the core board stacking structure. The resin printing range is precisely limited to the BGA pad projection area, and the printing thickness is designed based on the board thickness difference value obtained from FA testing;

[0050] A prefabricated FA verification plate is used to measure the actual plate thickness difference ΔH and establish a compensation model:

[0051] ΔH = H reference - (H measured + δ), where δ is the process allowance of 0.05-0.15mm;

[0052] Correct the measured deviation through process allowance δ to avoid excessive thickness caused by overcompensation;

[0053] Resin printing should cover at least two adjacent GND layers, and the thickness of a single layer should be controlled at 5-15μm;

[0054] Resin printing covering adjacent GND layers balances interlayer stress and reduces warpage;

[0055] Resin printing adopts screen printing method, screen mesh number is 200-400 mesh, printing accuracy is ±0.02mm;

[0056] Fine screen ensures that the resin accurately covers the BGA projection area, reducing position deviation;

[0057] c. Use press temperature to pre-bake the resin;

[0058] Resin baking adopts segmented temperature control:

[0059] The first stage is 80-100℃ / 30-45min to eliminate solvent volatilization;

[0060] The second stage is 120-135℃ / 60-90min to complete the resin cross-linking and curing;

[0061] The staged heating prevents the resin from forming a crust on the surface, ensuring complete internal curing. The slow heating reduces the thermal expansion difference between the core board and the resin interface, thereby improving the interface bonding strength.

[0062] d. After the browning process is completed, the pressing process begins;

[0063] The outer layer production process includes:

[0064] a. Drilling, electroplating and back drilling after pressing;

[0065] When back-drilling, the drilling depth tolerance is controlled at ±0.075mm, and the residual column height is ≤0.25mm;

[0066] Residual column height control reduces signal reflection and insertion loss;

[0067] b. After implementing resin plugging, secondary electroplating is performed to form a POFV structure;

[0068] Resin plug holes are filled in two steps:

[0069] Step 1: Vacuum plugging, vacuum degree -0.08MPa to -0.1MPa, to eliminate bubbles;

[0070] Step 2: Pressure filling, pressure 0.3-0.5MPa, to ensure the density of the hole;

[0071] The synergistic effect of vacuum and pressure results in a high resin filling rate in the hole, and step-by-step control prevents resin overflow and improves the flatness of the hole mouth.

[0072] The thickness of secondary electroplated copper is controlled at 15-25μm, the hole copper thickness is ≥25μm, and thick hole copper ensures the mechanical strength of the hole wall;

[0073] c. After the outer layer pattern is completed, solder mask processing, character printing and surface treatment are carried out in sequence;

[0074] The surface treatment adopts immersion gold process, the nickel layer thickness is 3-5μm, the gold layer thickness is 0.05-0.1μm, and the immersion gold layer provides a stable welding surface;

[0075] d. Finally, the products are put into storage after molding, electrical testing and quality inspection.

[0076] The resin printing thickness is dynamically adjusted through FA testing to solve the problem of small board thickness caused by uneven pressing in the BGA area, and the thickness compensation accuracy is improved to ±5μm.

[0077] The resin material is epoxy-modified acrylic resin, and the CTE after curing is ≤50ppm / °C. The low CTE resin reduces thermal cycle stress and reduces the risk of delamination.

[0078] The present invention establishes a compensation model by laminating the FA verification board and combines it with the dynamic adjustment of the resin printing thickness to solve the problem of uneven board thickness in the BGA area, avoid the phenomenon of empty solder joints in the chip, and at the same time improve the product signal delay and heat dissipation abnormality caused by copper plating.

[0079] The above description is merely illustrative of certain exemplary embodiments of the present invention. It goes without saying that those skilled in the art will be able to modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and description are illustrative in nature and should not be construed as limiting the scope of protection of the claims.

Claims

1. A method for solving the problem of small thickness of the BGA plate at the server, characterized in that: include: Inner layer production process and outer layer production process; The inner layer production process includes: a. After cutting, the inner layer pattern transfer and inner layer etching are carried out in sequence; b. After passing AOI inspection, resin printing is performed at the selected BGA position on the GND layer. The number of resin printing layers is determined based on the core board stacking structure. The resin printing range is precisely limited to the BGA pad projection area, and the printing thickness is designed based on the board thickness difference value obtained from FA testing; c. Use press temperature to pre-bake the resin; d. After the browning process is completed, the pressing process begins; The outer layer production process includes: a. Drilling, electroplating and back drilling after pressing; b. After implementing resin plugging, secondary electroplating is performed to form a POFV structure; c. After the outer layer pattern is completed, solder mask processing, character printing and surface treatment are carried out in sequence; d. Finally, the products are put into storage after molding, electrical testing and quality inspection.

2. A method for solving the problem of small thickness of the server BGA plate according to claim 1, characterized in that: In step b of the inner layer production process, a pressed FA verification plate is pre-made, and the actual plate thickness difference value ΔH is measured using the pressed FA verification plate to establish a compensation model: ΔH = Hreference - (Hmeasured + δ), where δ is the process margin of 0.05-0.15 mm.

3. The method for solving the problem of small thickness of the server BGA plate according to claim 1, characterized in that: In step b of the inner layer production process, the resin printing covers at least two adjacent GND layers, and the thickness of a single layer printing is controlled at 5-15 μm.

4. The method for solving the problem of small thickness of the server BGA plate according to claim 1, characterized in that: In step b of the inner layer production process, the resin is printed using screen printing, with a screen mesh size of 200-400 meshes and a printing accuracy of ±0.02mm.

5. The method for solving the problem of small thickness of the server BGA plate according to claim 1, characterized in that: In step c of the inner layer production process, resin baking adopts segmented temperature control: 80-100°C / 30-45 minutes in the first stage and 120-135°C / 60-90 minutes in the second stage.

6. The method for solving the problem of small thickness of the server BGA plate according to claim 1, characterized in that: In step a of the outer layer production process, during back drilling, the drilling depth tolerance is controlled within ±0.075 mm, and the residual column height is ≤0.25 mm.

7. The method for solving the problem of small thickness of the server BGA plate according to claim 1, characterized in that: In step b of the outer layer production process, the resin plug holes are filled in two steps: Step 1: Vacuum plugging, vacuum degree -0.08MPa to -0.1MPa, to eliminate bubbles; Step 2: Pressure filling, pressure 0.3-0.5MPa, to ensure the density of the hole.

8. The method for solving the problem of small thickness of the server BGA plate according to claim 1, characterized in that: In step b of the outer layer production process, the secondary electroplating copper thickness is controlled at 15-25 μm, and the hole copper thickness is ≥25 μm.

9. The method for solving the problem of small thickness of the server BGA plate according to claim 1, characterized in that: In step c of the outer layer production process, the surface treatment adopts the gold immersion process, the nickel layer thickness is 3-5 μm, and the gold layer thickness is 0.05-0.1 μm.

10. The method for solving the problem of small thickness of the server BGA board according to claim 1, characterized in that: The resin material is epoxy-modified acrylic resin, and the CTE after curing is ≤50ppm / °C.

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