Method for manufacturing a circuit board

Abstract

The present invention discloses a circuit board and a manufacturing method thereof. The manufacturing method includes the following steps: providing a circuit substrate, the circuit substrate including a substrate, a first circuit layer, and a first solder mask layer covering the surface of the first circuit layer, and a first solder mask opening exposing a part of the first circuit layer being formed on the first solder mask layer; forming a first copper layer in the first solder mask opening and on the surface of the first solder mask layer, the first copper layer including a first copper material layer located in the first solder mask opening and a second copper material layer located on the surface of the first solder mask layer, and the first copper material layer being higher than the plane where the first solder mask layer is located; grinding the first copper layer until the first solder mask layer is exposed, and the first copper material layer is flush with the first solder mask layer; printing solder paste on the ground first copper material layer, and then performing reflow soldering to form solder balls. By filling copper in the circuit substrate with a solder mask opening and keeping the filled copper surface flush with the solder mask layer after grinding, the present invention can solve the problem of solder ball breakage.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit boards, and particularly to a circuit board and a manufacturing method thereof. Background Art

[0002] The current soldering process for FC-CSP (Flip Chip Chip Scale Package) and FC-BGA (Flip Chip Ball Grid Array) is generally as follows: on the outer layer circuit with a solder mask layer, solder paste is directly printed in the solder mask openings formed in the solder mask layer, and then after reflow soldering, the solder paste aggregates into balls and is welded to the copper surface. When performing client packaging, the solder on the substrate forms an IMC (Intermetallic compound) layer with the copper at the welding point. The IMC layer ages over time from Cu 6 Sn 5 with good reliability and strong welding strength, and gradually generates Cu 3 Sn with poor reliability. After physical collision or stretching, the problem of bump crack is likely to occur. In the high-temperature reflow soldering process, due to the different thermal expansion coefficients of copper, tin, and the solder mask layer, stress pulling will occur when packaging solder joints at high temperature, which is also likely to cause the problem of bump crack. Summary of the Invention

[0003] In view of this, it is necessary to provide a circuit board and a manufacturing method thereof that can solve the above technical problems.

[0004] The first aspect of the present application provides a manufacturing method of a circuit board, including the following steps:

[0005] Provide a circuit substrate, where the circuit substrate includes a substrate, a first circuit layer formed on the substrate, and a first solder mask layer covering the surface of the first circuit layer, and a first solder mask opening exposing the first circuit layer is formed in the first solder mask layer;

[0006] Form a first copper layer in the first solder mask opening and on the surface of the first solder mask layer. The first copper layer includes a first copper material layer located in the first solder mask opening and a second copper material layer located on the surface of the first solder mask layer, and the first copper material layer is higher than the plane where the first solder mask layer is located;

[0007] Grind the first copper layer until the first solder mask layer is exposed, and make the first copper material layer in the first solder mask opening flush with the first solder mask layer;

[0008] Print first solder on the ground first copper material layer, and then perform reflow soldering.

[0009] According to some embodiments of the present application, the grinding includes physical grinding and chemical grinding. The copper layer is coarsely ground by physical grinding, and then finely ground by chemical grinding, which improves the grinding efficiency and ensures that the ground copper layer has a small roughness.

[0010] According to some embodiments of the present application, physical grinding is performed using a grinding machine with a flatness < 3 μm, and then chemical grinding is performed using a grinding fluid until the surface roughness Ra of the first copper material layer after grinding is < 0.3 μm.

[0011] According to some embodiments of the present application, physical grinding is performed using a disk rotary grinding machine, and chemical grinding is performed using a disk rotary grinding machine in combination with a grinding fluid. Among them, the grinding fluid can be, for example, a mixture formed by SiO 2 , CeO 2 and water. It can be understood that grinding fluids with other components can also be used.

[0012] According to some embodiments of the present application, the steps of forming the first copper layer include: first leveling the copper on the circuit board, and then plating copper by vertical continuous plating (VCP). First, rapid copper deposition is performed by leveling the copper, and then the entire board is plated with copper by the VCP method, which can quickly form the first copper layer.

[0013] According to some embodiments of the present application, the first solder mask opening is a blind hole, and the ratio of its aperture to its depth is greater than 1.5.

[0014] According to some embodiments of the present application, the height difference between the plane of the first copper material layer and the plane of the first solder mask layer is ≥ 5 μm. That is, the first copper material layer is 5 μm or more higher than the first solder mask layer.

[0015] According to some embodiments of the present application, before printing the solder paste, it further includes surface treatment of the ground first copper material layer. The method of surface treatment of the first copper material layer is beneficial to subsequent printing of the solder paste on its surface and improves the bonding force between the solder paste and the first copper material layer.

[0016] According to some embodiments of the present application, the circuit board further includes a second circuit layer formed on the substrate. The second circuit layer and the first circuit layer are respectively located on opposite surfaces of the substrate. A second solder mask layer is covered on the surface of the second circuit layer, and a second solder mask opening exposing the second circuit layer is opened in the second solder mask layer. The manufacturing method further includes:

[0017] A second copper layer is formed within the second solder mask opening and on the surface of the second solder mask layer. The second copper layer includes a third copper material layer within the second solder mask opening and a fourth copper material layer on the surface of the second solder mask layer. The third copper material layer is higher than the plane where the second solder mask layer is located.

[0018] The second copper layer is ground until the second solder mask layer is exposed, and the third copper material layer within the second solder mask opening is flush with the second solder mask layer.

[0019] A second solder is printed on the ground third copper material layer, and then reflow soldering is performed.

[0020] According to some embodiments of the present application, the step of grinding the second copper layer is: physically grinding using a grinding machine with a flatness < 3μm, and then chemically grinding using a grinding fluid until the surface roughness Ra of the ground third copper material layer < 0.3um.

[0021] According to some embodiments of the present application, after grinding, it further includes a step of water washing to remove the grinding fluid.

[0022] According to some embodiments of the present application, the first solder and the second solder are solder pastes.

[0023] The second aspect of the present application provides a circuit board, including:

[0024] A circuit board substrate, which includes a substrate, a first circuit layer formed on the substrate, and a first solder mask layer covering the surface of the first circuit layer. A first solder mask opening exposing the first circuit layer is formed on the first solder mask layer;

[0025] A first copper material layer, filled within the first solder mask opening and flush with the first solder mask layer;

[0026] A first solder, disposed on the first copper material layer.

[0027] According to some embodiments of the present application, the circuit board further includes:

[0028] A second circuit layer, formed on opposite sides of the substrate from the first circuit layer;

[0029] A second solder mask layer, covering the surface of the second circuit layer. A second solder mask opening exposing the second circuit layer is formed on the second solder mask layer;

[0030] A third copper material layer, filled within the second solder mask opening and flush with the second solder mask layer;

[0031] A second solder, disposed on the third copper material layer.

[0032] In the manufacturing method provided in the embodiments of the present application, by forming a first copper layer in the first solder mask opening and on the first solder mask layer, and grinding and polishing the first copper layer, the solder mask opening is filled, and a first copper material layer with the same height as the plane where the first solder mask layer is located is formed. When performing solder paste printing and reflow soldering, the stress pulling force caused by the different coefficients of thermal expansion between the solder mask layer and copper and tin can be reduced, and thus solder ball fracture is less likely to occur. In addition, in the existing method of directly printing solder paste in the solder mask opening formed in the solder mask layer, the thickness of the solder paste includes the thickness of the solder paste filled in the solder mask opening and the thickness of the solder paste protruding above the solder mask layer. By filling copper in the solder mask opening in the present application, the total thickness of the subsequent printed solder paste is reduced, the cost of the solder paste is saved, and the pulling torque during encapsulation can be shortened, making solder ball fracture even less likely to occur. By filling copper in the circuit board substrate with a solder mask opening and keeping the filled copper surface flush with the solder mask layer after grinding, a circuit board substrate with a flat copper surface at the solder mask opening is formed, which can solve the problem of solder ball fracture. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 FIG. is a schematic structural diagram of a circuit board substrate provided by an embodiment of the present application;

[0034] Figure 2 On Figure 1 Schematic structural diagram of forming a first copper layer and a second copper layer on the circuit board substrate;

[0035] Figure 3 For Figure 2 Schematic structural diagram after grinding the first copper layer and the second copper layer;

[0036] Figure 4 For Figure 3 Schematic structural diagram of forming a circuit board by reflow soldering a first solder and a second solder on the first copper material layer and the third copper material layer;

[0037] MAIN ELEMENT SYMBOL DESCRIPTION

[0038]

[0039] The following specific embodiments will further illustrate the present invention in conjunction with the above-mentioned drawings. SPECIFIC EMBODIMENTS

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used in the specification of this invention are for the purpose of describing specific embodiments only and are not intended to limit the invention.

[0042] An embodiment of this application provides a method for manufacturing a circuit board, including the following steps:

[0043] Step S1, refer to Figure 1 , and provide a circuit board substrate 10.

[0044] In one embodiment, the circuit board substrate 10 includes a substrate 100 and a first circuit layer 110 and a second circuit layer 210 formed on opposite surfaces of the substrate 100. A first solder mask layer 120 is covered on the surface of the first circuit layer 110, and a second solder mask layer 220 is covered on the surface of the second circuit layer 210. A first solder mask opening 130 exposing a part of the first circuit layer 110 is formed on the first solder mask layer 120, and a second solder mask opening 230 exposing a part of the second circuit layer 210 is formed on the second solder mask layer 220.

[0045] In this example, the first circuit layer 110 includes a first layer of circuit 111 and a second layer of circuit 112. The upper surface of the first layer of circuit 111 and the lower surface of the second layer of circuit 112 are electrically connected through a first conduction structure 113, and in other areas, the lower first layer of circuit 111 and the upper second layer of circuit 112 are separated by an insulating layer 300. The material of the insulating layer 300 includes but is not limited to epoxy resin, etc. In some embodiments, the materials of the first layer of circuit 111, the second layer of circuit 112, and the first conduction structure 113 are copper. Similarly, the second circuit layer 210 includes a third layer of circuit 211 and a fourth layer of circuit 212. The lower surface of the third layer of circuit 211 and the upper surface of the fourth layer of circuit 212 are electrically connected through a second conduction structure 213, and the upper third layer of circuit 211 and the lower fourth layer of circuit 212 are separated by the insulating layer 300. It can be understood that in this example, a two-layer circuit layer stack is taken as an example for illustration, and in practice, the number of stacked layers can be selected according to needs, and the stacking method is an existing method, which will not be elaborated here.

[0046] In some embodiments, taking the preparation of the first solder mask layer 120 as an example, first form a solder mask layer on the substrate 100 on which the first circuit layer 110 is formed, then cover a photosensitive dry film on the solder mask layer for exposure, then develop it with a 1% sodium carbonate solution, and finally remove the photosensitive dry film to form the first solder mask layer 120 with the first solder mask opening 130.

[0047] In some embodiments, the opening sizes of the first solder mask opening 130 and the second solder mask opening 230 are > 45 μm. When the solder mask opening is a through hole, the opening size refers to the diameter of the through hole.

[0048] After the first solder mask layer 120 is prepared, in some embodiments, it further includes a step of plasma treatment, using CF 4 and O 2 as working gases, and using the generated plasma to perform surface cleaning and roughening of the solder mask on the formed circuit board 10.

[0049] Step S2, please refer to Figure 2 , form a first copper layer 140 in the first solder mask opening 130 and on the first solder mask layer 120, and form a second copper layer 240 in the second solder mask opening 230 and on the second solder mask layer 220.

[0050] Among them, the first copper layer 140 includes a first copper material layer 141 located in the first solder mask opening 130 and a second copper material layer 142 located on the surface of the first solder mask layer 120. The second copper layer 240 includes a third copper material layer 241 located in the second solder mask opening 230 and a fourth copper material layer 242 located on the surface of the second solder mask layer 220. Among them, the first copper material layer 141 is higher than the plane where the first solder mask layer 120 is located, and the third copper material layer 241 is higher than the plane where the second solder mask layer 220 is located, so as to grind the first copper material layer 141 and the third copper material layer 241 respectively later.

[0051] In some embodiments, the first copper layer 140 and the second copper layer 240 can be formed simultaneously. Specifically, in some embodiments, taking the formation of the first copper layer 140 as an example, a leveling copper process can be used for the circuit board 10, electroplate 0.5 μm - 0.7 μm thick copper, and then perform vertical continuous plating (VCP). When electroplating, use filling hole solution, and after electroplating copper, the first copper material layer 141 filled in the first solder mask opening 130 is higher than the first solder mask layer 120 by ≥ 5 μm. In some embodiments, the first solder mask opening 130 is a through hole, and the ratio of its aperture to its depth is greater than 1.5.

[0052] Step S3, refer to Figure 3 , grind the first copper layer 140 until the first solder mask layer 120 is exposed, and after grinding the first copper material layer 141 formed in the first solder mask opening 130, it is basically flush with the exposed first solder mask layer 120. Grind the second copper layer 240 until the second solder mask layer 220 is exposed, and after grinding the third copper material layer 241 formed in the second solder mask opening 230, it is basically flush with the exposed second solder mask layer 220.

[0053] In some embodiments, the grinding methods include physical grinding and chemical grinding. In some embodiments, physical grinding is carried out in the following manner: using a disk rotary grinding machine with a flatness < 3um, and the non-woven grinding wheel used has a mesh number of 80. Grinding is performed until there is a remaining thickness of 2um from the target thickness. Then chemical grinding is carried out: using a disk-type CMP device, and using a chemical grinding fluid (main components: SiO 2 +CeO 2 (10 - 30%) + deionized water (70%) and a polishing pad (polyurethane) for polishing. The following purposes are achieved through the chemical grinding process: a. achieving the final required thickness; b. removing the copper burrs generated by physical grinding; c. making the surface roughness Ra of the copper surface < 0.3um.

[0054] In some embodiments, after the above physical and chemical grinding, a horizontal water washing line is used to perform a full-board cleaning on the ground circuit board to thoroughly wash away the chemical grinding fluid. The purpose of water washing is to wash away the grinding products of the target product, and after water washing, it is dried and the surface is reserved for use.

[0055] In some embodiments, after grinding and water washing, surface treatment is further included for the remaining first copper material layer 141 and the third copper material layer 241. The surface treatment methods include but are not limited to tin plating, OSP (organic solder mask) surface treatment, nickel palladium gold surface treatment, etc.

[0056] Step S4, refer to Figure 4 , solder paste is printed on the ground first copper material layer 141, and after reflow soldering, a first solder 143 is formed. Solder paste is printed on the third copper material layer 241, and then after reflow soldering, a second solder 243 is formed.

[0057] In some embodiments, after reflow soldering, a de-fluxing process is carried out.

[0058] Refer to Figure 4 , an embodiment of the present application further provides a circuit board, including a circuit board 10, a first copper material layer 141, and a first solder 143. Among them, the circuit board 10 includes a substrate 100, a first circuit layer 110, and a first solder mask layer 120. The first circuit layer 110 is formed on one side surface of the substrate 100, the first solder mask layer 120 covers the surface of the first circuit layer 110, and the first solder mask layer 120 is provided with a first solder mask opening 130 that exposes a part of the first circuit layer 110. The first copper material layer 141 is filled in the first solder mask opening 130 and is substantially flush with the plane where the first circuit layer 110 is located. The first solder 143 is formed on the first copper material layer 141.

[0059] In some embodiments, the circuit board further includes a second circuit layer 210, a second solder mask layer 220, a third copper layer 241, and a second solder 243. Among them, the second circuit layer 210 and the first circuit layer 110 are respectively formed on opposite sides of the substrate 100. The second solder mask layer 220 covers the surface of the second circuit layer 210 and is provided with a second solder mask opening 230 exposing the second circuit layer 210. The third copper layer 241 is filled in the second solder mask opening 230 and is substantially flush with the plane where the second circuit layer 210 is located. The second solder 243 is formed on the third copper layer 241.

[0060] In this application, by filling the solder mask opening with a copper layer flush with the solder mask layer, the influence of the thickness of the solder mask opening and the solder mask layer is eliminated. When performing solder paste printing and reflow soldering, the stress pulling force at high temperature caused by different coefficients of thermal expansion between the solder mask layer, copper, and solder can be reduced. Compared with directly printing solder paste in the solder mask opening, the total thickness of the solder paste used in this application is reduced, making the pulling torque shorter during encapsulation and less likely to cause solder ball fracture.

[0061] The above is only a preferred embodiment of the present invention and does not impose any formal limitations on the present invention. Although the present invention has been disclosed as a preferred embodiment above, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments by using the above-disclosed technical content without departing from the technical solution of the present invention. However, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for manufacturing a circuit board, characterized in that, it includes the following steps: Provide a circuit substrate, the circuit substrate includes a substrate, a first circuit layer formed on the substrate, and a first solder mask layer covering the surface of the first circuit layer, and a first solder mask opening exposing a part of the first circuit layer is formed on the first solder mask layer; Form a first copper layer in the first solder mask opening and on the surface of the first solder mask layer, the first copper layer includes a first copper material layer located in the first solder mask opening and a second copper material layer located on the surface of the first solder mask layer, and the first copper material layer is higher than the plane where the first solder mask layer is located; Grind the first copper layer until the first solder mask layer is exposed, and the first copper material layer formed in the first solder mask opening is flush with the first solder mask layer; Print a first solder on the ground first copper material layer, and then perform reflow soldering to form solder balls.

2. The method for manufacturing a circuit board according to claim 1, characterized in that, the grinding includes physical grinding and chemical grinding.

3. The method for manufacturing a circuit board according to claim 2, characterized in that, Use a grinding machine with a flatness <3μm for physical grinding, and then use a grinding fluid for chemical grinding until the surface roughness Ra of the first copper material layer after grinding <0.3um.

4. The method for manufacturing a circuit board according to claim 1, characterized in that, The step of forming the first copper layer includes: first leveling the copper of the circuit substrate, and then plating copper by vertical continuous electroplating.

5. The method for manufacturing a circuit board according to claim 1, characterized in that, When forming the first copper layer, the height difference between the first copper material layer and the plane where the first solder mask layer is located ≥5μm.

6. The method for manufacturing a circuit board according to claim 1, characterized in that, Before printing the solder paste, it also includes surface treatment of the ground first copper material layer.

7. The method for manufacturing a circuit board according to any one of claims 1 to 6, characterized in that, The circuit substrate further includes a second circuit layer formed on the substrate, the second circuit layer and the first circuit layer are respectively located on two opposite surfaces of the substrate, a second solder mask layer is covered on the surface of the second circuit layer, and a second solder mask opening exposing a part of the second circuit layer is formed on the second solder mask layer, and the manufacturing method further includes: Form a second copper layer in the second solder mask opening and on the surface of the second solder mask layer, the second copper layer includes a third copper material layer located in the second solder mask opening and a fourth copper material layer located on the surface of the second solder mask layer, and the third copper material layer is higher than the plane where the second solder mask layer is located; Grind the second copper layer until the second solder mask layer is exposed, and the third copper material layer formed in the second solder mask opening is flush with the second solder mask layer; Print a second solder on the ground third copper material layer, and then perform reflow soldering.

8. The method for manufacturing a circuit board according to claim 7, characterized in that, The steps for grinding the second copper layer are as follows: physically grind using a grinding machine with a flatness < 3 μm, and then chemically grind using a grinding fluid until the surface roughness Ra of the third copper material layer after grinding is < 0.3 μm.

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