TW202114494A - Circuit structure having anti-laser gap-filling layer and method for making the same - Google Patents

Abstract

A circuit structure having anti-laser gap-filling layer includes a substrate, a circuit layer, a gap-filling layer and a solder resist layer. The circuit layer is formed on the substrate and has a first bonding pad and a second bonding pad. The gap-filling layer is filled between the first and second bonding pads. The solder resist layer partially covers the circuit layer and has a solder resist opening where at least a part of the first and second bonding pads and the gap-filling layer is exposed, in which the thickness of the solder resist layer which can be burned through by a laser beam per unit time is higher than that of the gap-filling layer which can be burned through by the same laser beam per unit time.

Description

Circuit structure with anti-laser gap filling layer and its manufacturing method

The invention relates to a method for manufacturing a circuit board, in particular to a method for manufacturing a circuit board with a window area.

The traditional circuit board structure usually forms a solder resist layer on the metal circuit layer to cover the circuits and metal surfaces that do not need to be soldered, so as to prevent short circuits during soldering and save the amount of solder; on the other hand, the solder resist layer It can prevent moisture and electrolyte from entering the circuit board to avoid oxidation of the circuit layer and harm the electrical properties, and also prevent the device from damaging the circuit layer. On the other hand, since the line width of the circuit layer on the circuit board is getting narrower and narrower, it can prevent The solder layer also provides insulation between adjacent circuits.

Then, a development etching process is used to remove the solder mask on the designated solder joints of the circuit layer, so that the circuit layer of the solder joints are exposed, so as to facilitate the subsequent soldering process. The development and etching process uses UV light or visible light of a specific wavelength band on the solder mask to cure the solder mask; then a special chemical solvent is used to remove the uncured solder mask material to make the solder joint The circuit layer is exposed. However, when the solder mask is cured by light, because the reflectivity and thickness of the solder mask affect the penetration of UV or visible light, the solder mask at the bottom of the solder mask is not fully cured and is removed by a special chemical solvent. . In this way, the problem of overcut is prone to occur during the development process, and the circuit layer that should be protected by the solder mask is exposed. When the subsequent soldering process is performed, it is likely to cause a short circuit or even damage the circuit board. On the other hand, in the subsequent soldering process, the adjacent pads are also prone to short circuits due to the small spacing.

In view of this, the main purpose of the present invention is to provide a light emitting diode carrier board manufacturing process, which can accurately expose the predetermined exposed circuit layer, while taking into account the smaller pad spacing and reducing the risk of short circuit.

In order to achieve the above object, the present invention provides a circuit structure with an anti-laser gap filling layer, which includes a substrate, a circuit layer, a gap filling layer and a solder resist layer. The circuit layer is formed on the substrate, and the circuit layer has A first soldering pad and a second soldering pad. The seam filling layer is filled between the first and second soldering pads. The solder resist layer partially covers the circuit layer. The solder resist layer has a solder resist window. 2. At least a part of the solder pad and the seam filling layer is exposed in the solder mask window; wherein the thickness of the solder mask layer that can be burned through by the laser beam per unit time is greater than that of the solder mask layer which can be burned by the same intensity per unit time. The thickness that the beam burns through.

In order to achieve the above and other objectives, the present invention also provides a method for manufacturing a circuit structure with an anti-laser gap-filling layer, which includes:

A substrate is provided, a circuit layer is formed on the substrate, and the circuit layer has a first solder pad and a solder pad;

Fill a gap filling layer between the first and second solder pads;

Cover a solder mask on the circuit layer and the filling layer;

A laser beam is used to form a solder mask on the solder mask, so that at least a part of the first and second solder pads and the filling layer are exposed in the solder mask. The solder mask can be lightning-struck per unit time. The burn-through thickness of the laser beam is greater than the thickness of the caulking layer that can be burned through by the laser beam in a unit time.

The solder mask formed by laser engraving opens the window, and the window wall has good flatness, which can greatly improve the problem that the conventional development process is prone to over-etching; in addition, the present invention also produces unexpected effects in that, because it does not need to use The window is opened during the exposure and development process, so the selected solder mask material can be a dosage form that does not add a photo initiator, which can further reduce the material cost of the solder mask.

On the other hand, by deliberately making the solder mask and the caulking layer have different resistance to the laser beam, the caulking layer is selectively not easily burned through by the laser beam, so that the laser beam is windowed. At the same time, the degree of ablation of the seam filling layer is reduced, so that the seam filling layer remains between the first and second solder pads. When the first and second solder pads are subsequently electroplated on the surface, the seam filling layer can serve as both The retaining wall between the surface plating layers prevents the two surface plating layers from excessively narrowing the distance during the surface electroplating process and causing short circuit problems.

The circuit structure of the present invention can be a single-layer board structure or a multi-layer composite board structure, which can be a carrier board of a flexible printed circuit (FPC) or a carrier board of a printed circuit board (PCB). The material can be but not limited to polyethylene terephthalate (PET) or other polyester film, polyimide film, polyimide film, polypropylene film, polystyrene film.

Please refer to Figure 1. In the first embodiment of the present invention, a circuit layer 20 with a working surface 21 is first formed on a substrate 10. For example, a thin copper foil may be formed on the substrate 10 first. Copper is then plated to form a copper conductive layer, and then the copper conductive layer is imaged by a circuit image transfer technology to form the circuit layer 20 as described above. The circuit layer 20 has a first bonding pad 22 and a second bonding pad 23 with a gap 24 therebetween. The first and second bonding pads 22 and 23 can be used as electrical contacts for surface mount components such as light-emitting diode chips.

As shown in Figure 2, the circuit layer 20 is coated with a layer of caulking material, such as epoxy resin compound, which has better resistance to laser ablation. For example, the epoxy resin compound is mixed with titanium dioxide Ceramic materials such as powder or metal powder can improve the reflection ability of the laser beam, thereby achieving the purpose of anti-laser ablation. In a possible implementation manner, the gap-filling material is coated on the circuit layer 20 by screen printing, and then hardened; in other possible implementation manners, the gap-filling material is, for example, made into a dry film state in advance, and then used The laminator is laminated on the circuit layer 20.

Next, as shown in Figure 3, use a brushing wheel to remove the caulking material on the top surface of the circuit layer 20, leaving the caulking material in the gap 24 as the caulking layer 30. The top of the circuit layer 20 and the caulking layer 30 Face flush. In other possible embodiments, the gap-filling material can be directly filled into the gap by a dispenser, and then hardened into the gap-filling layer 30. In other possible embodiments, the circuit layer after brushing is additionally subjected to surface treatment to make the top surface slightly lower than the caulking layer. In other possible embodiments, the grinded gap filling layer is further subjected to surface treatment to make its top surface slightly lower than the circuit layer.

Next, as shown in Figure 4, a solder mask layer 40 is completely covered on the circuit layer 20 and the gap filling layer 30. In a possible embodiment, the solder mask layer 40 is coated on the circuit layer 20 by screen printing, for example. And the caulking layer 30, and then hardened. In other possible embodiments, the solder resist layer 40 is formed by, for example, laminating a semi-cured solder resist dry film on the circuit layer 20 and the gap filling layer 30 and then hardening it. In a possible embodiment, the material of the solder mask is mainly composed of thermosetting resin, light curing resin or a mixture of the two. In a possible embodiment, the composition of the solder mask does not contain a photoinitiator or a photocuring agent.

As shown in Figure 5, a laser engraving machine is used to emit a laser beam to form the required number of solder mask openings 41 on the solder mask layer 40, so that the first and second solder pads 22, 23 and the gap filling layer 24 At least a part of the solder mask is not covered in the solder mask 41, and because the thickness of the solder mask 40 that can be burned through by the laser beam in a unit time is greater than that of the caulking layer that can be burned through by the laser beam in a unit time of 30 The thickness, that is, the seam filling layer 30 has better resistance to laser ablation, and because the laser beam must first burn through the solder mask layer 40 before it can touch the seam layer 30, it can ensure that the solder mask window 41 is formed At this time, the gap-filling layer 30 is still not burned through by the laser beam or only slightly ablated, that is, the laser beam can be controlled to selectively remove only the solder mask material but still largely retain the gap-filling material. In a possible implementation, the thickness of the solder mask layer that can be burned through by the laser beam per unit time is more than twice the thickness of the filling layer that can be burned through by the laser beam of the same intensity per unit time under the same conditions. That is, there is a significant gap between the anti-laser ablation capabilities of the solder mask layer and the gap filling layer, which improves the yield of the laser windowing step.

Finally, as shown in Figure 6, in the subsequent surface mounting process, the top surfaces of the first and second bonding pads 22, 23 of the circuit layer 20 can be further formed with first and second surface plating layers 25, 26, respectively. It can be, but is not limited to, one of a nickel layer, a gold layer, a silver layer, and a palladium layer or a laminated structure thereof, such as electroplated nickel-gold laminated structure, electroplated nickel-silver-gold laminated structure, electroplated nickel-silver laminated structure, electroless nickel-gold laminated structure, Chemical nickel-silver laminated structure or nickel-palladium-gold laminated structure. Since at least a part of the side surfaces of the first and second bonding pads 22, 23 are covered by the caulking layer 20, in the step of performing electroplating to form the first and second surface plating layers 25, 26, the first and second The surface plating layers 25, 26 mainly only grow in the thickness direction, and the growth in the horizontal plane is limited. This can ensure that the designed spacing between the first and second surface plating layers 25, 26 is still maintained, and the risk of short circuits after electroplating is greatly reduced. .

In summary, the present invention opens the window of the solder mask formed by laser engraving, and its window wall has good flatness, which can greatly improve the problem that the conventional development process is prone to over-etching; in addition, the present invention also produces unpredictable effects. Since there is no need to open the window by the exposure and development process, the selected solder mask material can be a dosage form that does not add a photo initiator, which can further reduce the material cost of the solder mask. On the other hand, by deliberately making the solder mask and the caulking layer have different resistance to the laser beam, the caulking layer is selectively not easily burned through by the laser beam, so that the laser beam is windowed. At the same time, the degree of ablation of the seam filling layer is reduced, so that the seam filling layer remains between the first and second solder pads. When the first and second solder pads are subsequently electroplated on the surface, the seam filling layer can serve as both The retaining wall between the surface plating layers prevents the two surface plating layers from excessively narrowing the distance during the surface electroplating process and causing short circuit problems. In other words, the manufacturing process disclosed in the present invention can reduce the material cost while improving the processing accuracy, which can indeed meet the needs of the industry.

10: substrate 20: circuit layer 21: working surface 22: The first pad 23: The second pad 24: gap 30: caulking layer 40: Solder mask 41: Weld-proof window

Figures 1 to 6 are schematic cross-sectional views of the manufacturing process of the first embodiment of the present invention.

10: substrate

20: circuit layer

21: working surface

22: The first pad

23: The second pad

24: gap

30: caulking layer

40: Solder mask

41: Weld-proof window

Claims (6)

A circuit structure with an anti-laser gap filling layer, including: A substrate; A circuit layer formed on the substrate, the circuit layer having a first bonding pad and a second bonding pad; A filling layer is filled between the first and second solder pads; and A solder mask layer partially covering the circuit layer, the solder mask layer has a solder mask window, and at least a part of the first and second solder pads and the seam filling layer are exposed in the solder mask window; Wherein, the thickness of the solder mask layer that can be burned through by the laser beam per unit time is greater than the thickness of the gap filling layer that can be burned through by the laser beam of the same intensity per unit time. The circuit structure with an anti-laser gap filling layer as described in claim 1, wherein the thickness of the solder mask layer that can be burned through by a laser beam per unit time is that the gap filling layer can be burned by a laser beam of the same intensity per unit time Burn through more than twice the thickness. The circuit structure with an anti-laser gap filling layer according to claim 1, wherein the circuit layer further includes a first surface plating layer and a second surface plating layer, and the first surface plating layer is formed on the top surface of the first bonding pad, The second surface plating layer is formed on the top surface of the second bonding pad. A manufacturing method of a circuit structure with an anti-laser gap-filling layer, including: Providing a substrate, forming a circuit layer on the substrate, the circuit layer having a first bonding pad and a second bonding pad; Fill a gap filling layer between the first and second solder pads; Covering the circuit layer and the seam filling layer with a solder resist layer; A laser beam is used to form a solder mask on the solder mask, so that at least a part of the first and second solder pads and the filling layer are exposed in the solder mask, wherein the solder mask unit The thickness that can be burned through by the laser beam in a time is greater than the thickness of the gap-filling layer that can be burned through by the laser beam in a unit time. According to claim 4, the method for manufacturing a circuit structure with an anti-laser caulking layer, wherein the thickness of the solder mask layer that can be burned through by the laser beam per unit time is the same intensity as the caulking layer can be burned per unit time The burn-through thickness of the laser beam is more than twice the thickness. According to the manufacturing method of the circuit structure with the anti-laser gap filling layer as described in claim 4, a first surface plating layer and a second surface plating layer are formed on the top surfaces of the first and second bonding pads, respectively.

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