TWI655883B - Circuit board and method for making thereof - Google Patents

Abstract

A circuit board structure comprising a substrate, a plurality of conductive traces, at least one wire finger, a seam layer and at least one surface plating layer, wherein the conductive traces and the wire fingers are formed on the surface of the substrate, adjacent conductive traces There is a gap between the wire fingers and the adjacent conductive traces, the gap layer is filled in the gaps, and the surface plating layer is formed on the top surface of the wire bonding finger, which may be a nickel layer, a gold layer, a silver layer, One of the palladium layers or the laminated structure thereof, wherein the surface plating layer has a top surface and at least one side surface, and at least a portion of the side surfaces does not contact the caulking layer. Thereby, the circuit board structure of the present invention has good solderability, is compatible with the wire bonding technology, and can increase the density of the wires.

Description

Circuit board structure and its manufacturing method

The present invention relates to a structure of a printed circuit board and a method of fabricating the same.

With the trend toward miniaturization of electronic products, circuit boards are also required to be made lighter and thinner, and traces of conductive traces and bonding fingers on the circuit board are increasingly denser, so the design and manufacturing facilities thereof The challenges are also getting higher and higher.

The smaller the gap between the fingers of the wire, the more likely the short circuit occurs during production. For example, in the past, Copper Defined Pad Design (also known as Non-Solder Mask Defined, NSMD for short) is used for surface plating on copper foil because the window of the solder resist layer is larger than the solder pad. When the nickel and gold layers 1 are coated on the three surfaces of the copper foil 2 (as shown in Fig. 11), the smaller the gap of the copper foil, the higher the risk of short circuit, and thus the demand for precision processing cannot be satisfied.

Another person uses a Solder Mask Defined (SMD) to limit the surface-plated nickel and gold layer 1 to the window of the solder resist layer 3 (as shown in Fig. 12). However, SMD has its inherent limitations in that the sides of the nickel and gold layers are completely covered by the solder mask, so that it is difficult to wire-bond the wafer to the wire fingers on the substrate by wire bonding, resulting in wire bonding. The yield of wire bonding technology is low. In addition, the use of SMD can also lead to poor solderability (only the top surface is the solder joint) and increase the difficulty of routing (copper foil 2 area is usually larger than the surface plating area).

In view of the above, the main object of the present invention is to provide a circuit board structure and a manufacturing method for fabricating a surface plating layer without SMD technology.

Another object of the present invention is to provide a circuit board structure and a manufacturing method capable of achieving both wire density and processing yield.

In order to achieve the above and other objects, the present invention provides a circuit board structure including a substrate, a plurality of conductive traces, at least one wire finger, a seam layer, and at least one surface plating layer, conductive traces and wire fingers. Formed on the surface of the substrate, between adjacent conductive traces or between the wire fingers and adjacent conductive traces, a gap layer is filled in the gaps, and a surface plating layer is formed on the top surface of the wire bonding finger, which can be It is a nickel layer, a gold layer, a silver layer, a palladium layer or a laminated structure thereof, wherein the surface plating layer has a top surface and at least one side surface, and at least a portion of the side surface does not contact the caulking layer.

In order to achieve the above and other objects, the present invention provides a method for fabricating a circuit board structure, comprising: forming a plurality of conductive traces on a surface of a substrate and at least one wire bonding finger, and having a gap between adjacent conductive traces, the soldering There is also a gap between the line finger and the adjacent conductive trace; coating the caulking material on the substrate, the conductive trace, the surface of the bonding wire finger and the gap; the conductive trace, the surface of the bonding wire finger The caulking material is removed, and the caulking material filled in the gaps is retained as a caulking layer; and a surface plating layer is formed on the top surface of the bonding wire finger, and the surface plating layer is a nickel layer, a gold layer, and a silver layer. And a laminated structure of the layer or the palladium layer, the surface plating layer having a top surface and at least one side surface, and at least a portion of the side surface does not contact the gap layer.

Based on the above design, the top surface and at least one side of the surface plating layer can be in contact with the solder, the solderability is good, and the side surface of the surface plating layer is unshielded, so that the circuit board structure of the present invention can still be compatible with the wire bonding technology (wire Bonding), and the filling layer filled in the gap can avoid the problem that the NSMD is easy to short-circuit due to the small gap, and the density of the wire is expected to increase.

Please refer to FIG. 1 , which is a cross-sectional view showing an embodiment of a circuit board structure according to the present invention. The circuit board structure includes a substrate 10 , a plurality of conductive traces 20 , a plurality of bonding wire fingers 30 , and a filling layer 40 . And a surface plating layer 50. The circuit board structure of this embodiment can be, for example, an IC carrier board for packaging.

The substrate 10 is made of an insulating material such as BT resin and ABF resin, and the substrate 10 is formed with through holes 11 formed on the surface of the through holes 11 to connect different surfaces of the substrate 10. A conductive trace 20 and a bonding finger 30 are formed on the surface of the substrate 10, wherein the bonding wire finger 30 is a portion of the wiring board structure that needs to be in contact with the solder, and the conductive trace 20 is not in contact with the solder in principle. The material used to make the conductive trace 20 and the wire finger 30 is copper. The adjacent conductive trace 20 and the wire finger 30 have a gap between the adjacent conductive trace 20 and the gap layer 40 is filled in the hole. The surface plating layer 50 is formed on the top surface of the bonding wire finger 30, and the surface plating layer 50 has a top surface 51 and at least one side surface 52, at least a portion of which does not contact the caulking layer 40. The surface plating layer 50 may be one of a nickel layer, a gold layer, a silver layer, and a palladium layer or a laminated structure thereof. For example, the surface plating layer may be a nickel gold laminated structure, a nickel silver gold laminated structure, a nickel silver laminated structure or Nickel palladium gold laminate structure.

In order to avoid the conductive traces 20 from being exposed, the circuit board structure may further include a solder resist layer 60 formed on the surface of the conductive traces 20 and a portion of the fillet layer 40. Both the caulking layer 40 and the solder resist layer 60 are insulating layers, for example, all made of a solder resist material; in other possible embodiments, the caulking layer 40 may be other insulating filling materials different from the solder resist layer 60. For example, epoxy resin, enamel resin, polyimide resin, phenol resin, fluororesin, ceria, alumina, and the like.

In a possible embodiment, a part of the wire finger of the circuit board structure may be completely covered by the solder resist layer, and at least a part of the side of the wire finger of the other part is exposed without being in contact with the solder resist layer and the caulking layer.

Hereinafter, an embodiment of the circuit board structure and the method of manufacturing the same according to the present invention will be described below with reference to the drawings.

As shown in FIG. 2, the substrate 10 on which the thin copper foil 5A is laminated is used as a starting material, and the substrate 10 is drilled to form a plurality of through holes 11 penetrating through different surfaces of the substrate 10 (as shown in FIG. 3). Then, copper plating is performed to form the surface copper 5B and the hole copper 5C on the surface of the thin copper foil 5A and the through hole 11 (as shown in FIG. 4), and then, as shown in FIG. 5, the surface copper 5B is formed by the line image transfer technique. And the thin copper foil 5A is imaged, wherein a part of the surface copper 5B and the thin copper foil 5A are used as the conductive traces 20, and the other part is used as the bonding wire fingers 30, and after being patterned, between the conductive traces 20 and the bonding wire fingers There is a gap between the 30 and the conductive traces 20.

As shown in Fig. 6, the solder resist material 6A fills the line gap, and the solder resist material 6A also covers the conductive trace 20 and the top surface of the bond finger 30. As shown in FIG. 7, the conductive trace 20 and the solder resist 6A on the top surface of the bonding wire finger 30 are brushed off by the brush grinding wheel 7A, and the solder resist material located in the gap is left as the caulking layer 40, which becomes the eighth layer. The state shown in the figure.

As shown in FIG. 9, a solder resist layer 60 is covered on the top surface of the conductive trace 20 and a portion of the fillet layer 40, and the top surface of the solder wire finger 30 remains bare.

Next, a surface plating treatment is performed to form a surface plating layer 50 on the top surface of the bonding wire finger 30, and a part of the top surface 51 and the side surface 52 of the surface plating layer 50 is exposed without contacting the caulking layer 40 and the solder resist layer 60. Figure 1 shows the circuit board structure.

Based on the above design, the top surface and at least one side of the surface plating layer can be in contact with the solder, the solderability is good, and the side surface of the surface plating layer is unshielded, so that the circuit board structure of the present invention can still be compatible with the wire bonding technology (wire Bonding), and the filling layer filled in the gap can avoid the problem that the NSMD is easy to short-circuit due to the small gap, and the density of the wire is expected to increase.

In addition, please refer to FIG. 10 and FIG. 11 , wherein FIG. 10 discloses another embodiment of the present invention, and FIG. 11 is a conventional circuit board structure made by using NSMD technology. After comparison, it can be found that the same line spacing is obtained. Under the NSMD technology, it is very easy to cause the adjacent nickel, gold layer 1 and other surface plating layers to be too close, which significantly increases the risk of short circuit, resulting in an increase in the defect rate. In contrast, the present invention fills the line gap with the filling layer 40 first. After the surface plating, the risk of short circuit can be avoided. In other words, compared with the NSMD technology, the invention is more suitable for the circuit board structure design with high line density, and thus is more suitable for the design requirements and trends of the light and thin electronic products.

1‧‧‧ Nickel and gold layers

2‧‧‧ copper foil

3‧‧‧ solder mask

5A‧‧‧thin copper foil

5B‧‧‧ face copper

5C‧‧‧ hole copper

6A‧‧‧solderproof material

7A‧‧‧Brush wheel

10‧‧‧Substrate

11‧‧‧through holes

20‧‧‧ conductive traces

30‧‧‧welding line fingers

40‧‧‧Seam layer

50‧‧‧Surface plating

51‧‧‧ top surface

52‧‧‧ side

60‧‧‧ solder mask

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view showing an embodiment of a circuit board structure of the present invention.

2 to 9 are cross-sectional views showing a manufacturing process of one embodiment of the wiring board structure of the present invention.

Figure 10 is a cross-sectional view showing another embodiment of the circuit board structure of the present invention.

Figure 11 is a cross-sectional view showing a conventional circuit board structure processed by NSMD.

Fig. 12 is a cross-sectional view showing the structure of a circuit board which has been conventionally processed by SMD.

Claims (8)

A circuit board structure comprising: a substrate; a plurality of conductive traces formed on a surface of the substrate, having a gap between the adjacent conductive traces; at least one wire finger formed on the surface of the substrate, the wire finger Between adjacent conductive traces having a gap; a filling layer filled in the gaps; and at least one surface plating layer formed on the top surface of the bonding wire, the surface plating layer is a nickel layer, a gold layer Or a laminated structure of the silver layer or the palladium layer, the surface plating layer has a top surface and at least one side surface, and at least a portion of the side surface does not contact the gap layer, and the surface plating layer further has a Not touching the bottom surface of the caulking layer. The circuit board structure of claim 1, further comprising a solder resist layer formed on the surface of the conductive trace and a portion of the gap layer, and at least a portion of the side surface does not contact the solder resist layer. The circuit board structure of claim 2, wherein the solder resist layer and the caulking layer are both made of a solder resist material. The circuit board structure of any one of claims 1 to 3, wherein the conductive trace and the wire finger are both made of copper. A method for manufacturing a circuit board structure includes: forming a plurality of conductive traces and at least one wire fingers on a surface of a substrate, wherein a gap is formed between adjacent conductive traces, the wire fingers and adjacent conductive traces There is also a gap therebetween; a sealing material is applied to the substrate, the conductive traces, the surface of the bonding wire fingers, and the gaps; Removing the conductive traces and the caulking material on the surface of the bonding wire fingers, leaving the caulking material filled in the gaps as a caulking layer; and forming a surface plating layer on the top surface of the bonding wire fingers, The surface plating layer is one of a nickel layer, a gold layer, a silver layer, and a palladium layer, or a laminated structure thereof, the surface plating layer has a top surface and at least one side surface, and at least a portion of the side surface does not contact the caulking layer a layer, and the surface plating layer further has a bottom surface that is not in contact with the gap layer. The method of manufacturing the circuit board structure of claim 5, wherein before forming the surface plating layer, further comprising: forming a solder resist layer on the surface of the conductive trace and a portion of the gap layer, and at least the side surface Some of them did not touch the solder mask. The method of fabricating a circuit board structure according to claim 6, wherein the solder resist layer and the caulking layer are both made of a solder resist material. The method of fabricating a circuit board structure according to any one of claims 5 to 7, wherein the conductive trace and the wire finger are both made of copper.