CN102054712A - Method for controlling surface roughness of circuit board - Google Patents

Abstract

The invention discloses a method for controlling the surface roughness of a circuit board. When the existing circuit board is subjected to the second electroplating operation, since the current electroplating generally adopts the operation of direct copper plating and gold plating, after electroplating, the gold surface or copper surface relatively smooth, resulting in insufficient surface roughness of the circuit board, and the problem of poor wire bonding ability often occurs. The present invention operates as follows: when the circuit board is electroplated, the following steps are adopted: the operation of copper plating; the process of nickel plating To operate; to perform the operation of gilding. The roughness of the gold surface can be increased, thereby enhancing the bonding ability of the gold wire, and at the same time, the problem of appearance defects caused by it can be solved.

Description

A method for controlling the surface roughness of circuit board

technical field

The invention belongs to the field of substrate production, in particular to a method for controlling the surface roughness of a circuit board.

Background technique

During the production process of the substrate, especially when the pad operation of the wire bonding of the chip-scale package is required in the post-process, it is necessary to maintain a certain roughness on the surface of the substrate to ensure a strong wire bonding capability.

At present, for example, in the production process of TAPP (ultra-thin chip level package substrate), when the substrate is subjected to the second electroplating operation, since the current electroplating generally adopts direct copper plating and gold plating operations, the copper surface or gold surface after electroplating is usually Relatively smooth, resulting in insufficient surface roughness of the substrate, often resulting in poor wire bonding capabilities. It is difficult to meet the customer's requirements, and the resulting appearance defects are also relatively obvious, and the prior art does not provide a good solution to these problems.

Contents of the invention

In order to solve the problems in the prior art that the surface roughness of the substrate is not enough and the ability of wire bonding is often poor, the invention provides a method for controlling the surface roughness of the circuit board.

The method of the present invention is specifically:

When electroplating the substrate, the following steps are used:

Copper plating operation;

carry out nickel plating operations;

Perform gold-plating operations.

More preferably, the copper is bright copper.

More preferably, after bright copper plating, the operation of dumb copper plating is also included.

More preferably, the thickness of the dumb copper after electroplating is controlled between 9-12um.

More preferably, the operation of gold plating is specifically as follows:

First of all, the operation of flash gold plating is carried out;

Then carry out the operation of thick gold plating.

More preferably, the gold flash plating operation is: directly plating gold flash on the nickel layer, and the thickness of the flash gold is less than 0.2um.

More preferably, the thickness of the nickel layer after nickel electroplating is controlled between 5-9um.

Through the method of the present invention, the roughness of the gold surface can be increased, thereby enhancing the bonding ability of the gold wire, and at the same time, the problem of appearance defects generated thereby can be solved.

Description of drawings

Fig. 1 is a flowchart of the implementation method of the present invention;

Figure 2 is an experimental diagram of the influence of the change of the thickness of the dumb copper on the surface roughness of the substrate;

Fig. 3 is an experimental diagram of the influence of nickel-copper thickness variation on the surface roughness of the substrate.

Detailed ways

Specific embodiments of the present invention will be described below in conjunction with the accompanying drawings.

After the production of the substrate is completed, follow-up operations will be carried out, one of which is the need for wire bonding. Whether the wire bonding capability meets the standard needs to be verified by the substrate on the wire bonding equipment. The main operation is to put gold wires on the gold pads. Pull the gold wire on the pad with different strengths using the special pull hook for the equipment. When the strength required by the customer is used to pull the gold surface without peeling off, it means that the bonding ability is up to standard. If the surface roughness of the substrate is not enough, the bonding ability is often poor during the bonding process. Therefore, the purpose of the present invention is to optimize the electroplating process during the second electroplating, which can control the roughness of the substrate surface, solve the problem of poor wire bonding ability, and make the wire bonding ability meet the requirements of different customers.

Example 1:

In order to solve the problem of poor surface roughness of the substrate, the following plating sequence is used in the second plating:

Copper plating is performed first;

Then carry out the operation of nickel plating;

Finally, the gold plating operation is carried out.

Keeping the thickness of the nickel layer at 5-9um during the nickel plating operation is conducive to controlling the roughness within the expected range, especially the nickel layer with a thickness of 6-8um has a more obvious reflection on the roughness, so it can basically solve the surface problem. The problem of poor roughness.

Example 2:

In order to better solve the problem of poor surface roughness of the substrate, the following electroplating method can be used in this embodiment:

Copper plating operation;

carry out nickel plating operations;

Carry out flash gold plating operations;

Thick gold plating is performed.

The electroplating here is done by flash gold and thick gold. The flash gold is directly plated on the nickel layer, because the bonding force between the flash gold and the nickel surface is better, but the flash gold is very thin, generally less than 0.2um. In order to make the gold surface The bonding ability is good, which is achieved here by thick gold plating.

When performing the above electroplating, perform electroplating according to the parameters in the table below.

Through the above electroplating process, especially after flash gold and thick gold electroplating, the roughness of the gold surface can be effectively improved, and the problem of the roughness of the gold surface can also be solved.

Example 3:

In order to better solve the problem of poor surface roughness of the substrate, as shown in Figure 1, the following plating sequence is used in the second plating:

Perform bright copper plating operations;

Perform dumb copper plating operation;

carry out nickel plating operations;

Carry out flash gold plating operations;

Thick gold plating is performed.

The biggest difference between bright copper and dumb copper is the appearance and roughness of the copper surface after electroplating. Generally, the surface of bright copper is smoother and flatter, while the surface of dumb copper is rougher, with more pits and pits, which is more conducive to the control of roughness. Adjustment.

When electroplating, perform electroplating according to the parameters in the table below.

Through the above electroplating process, the operation of electroplating dumb copper is added. In order to control the range of the roughness of the gold surface, we use the method of controlling the thickness of the dumb copper to control the roughness of the gold surface.

The dumb copper layer is the main source of the roughness of the TAPP board, the nickel layer has a certain leveling effect on the dumb copper layer, and the gold layer is an intuitive performance of the roughness. The roughness of the gold surface has an extremely important influence on the quality of the wire bonding performance.

的范围时，金线的键合能力最好，并且能使TAPP产品较好通过AFI(自动光学检测)进行终检。After the dumb copper layer is added, the roughness of the gold surface can be increased. When the roughness value of the gold surface is

When the range of the gold wire is the best, the bonding ability of the gold wire is the best, and it can make the TAPP products pass the final inspection of AFI (automatic optical inspection) better.

The dumb copper newly used in the present invention can be prepared by using the bath solution prepared by the LP-1 dumb copper brightener produced by Schleich Chemical, which is common on the market, and its coating has a good effect of roughening the copper surface.

The roughness of the gold surface is measured using a step tester "Alpha step IQ surface profiler".

的范围内。实验效果如图1所示。After a series of DOE experiments, we found that when the thickness of dumb copper is controlled at 9-12um, the roughness can be basically maintained at

In the range. The experimental results are shown in Figure 1.

In addition, it is also found through experiments that the thickness variation of the nickel layer also has a certain contribution to the roughness. When the thickness of the nickel layer is 5-9um, it is beneficial to control the roughness within the expected range, especially for the nickel layer with a thickness of 6-8um, the reflection of the roughness is more obvious. The thickening of the nickel layer helps to cover up the roughness produced by the dumb copper and reduces the roughness reflected on the gold surface. The experimental results are shown in Figure 2.

Through the above-mentioned method of the present invention, the roughness of the gold surface can be increased, thereby enhancing the bonding ability of the gold wire, and at the same time, the problem of appearance defects generated thereby can be solved.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and equivalent technologies thereof, the present invention also intends to include these modifications and variations.

Claims (7)

1. A method for controlling the surface roughness of a circuit board, characterized in that, when the substrate is electroplated, the steps are as follows: Copper plating operation; carry out nickel plating operations; Perform gold-plating operations. 2. The method for controlling the surface roughness of a substrate according to claim 1, wherein the copper is bright copper. 3. The method for controlling the surface roughness of a substrate according to claim 2, characterized in that: after bright copper plating, the operation of dull copper plating is also included. 4. The method for controlling the surface roughness of the substrate according to claim 3, characterized in that: the thickness of the dumb copper after electroplating is controlled between 9-12um. 5. The method for controlling the surface roughness of a substrate as claimed in claim 1-4, wherein the operation of performing gold plating is specifically: First of all, the operation of flash gold plating is carried out; Then carry out the operation of thick gold plating. 6 . The method for controlling the surface roughness of a substrate according to claim 5 , wherein the gold flash plating operation is: directly plating gold flash on the nickel layer, and the thickness of the gold flash is less than 0.2 um. 7 . 7. The method for controlling the surface roughness of the substrate according to claim 6, characterized in that: the thickness of the nickel layer after nickel electroplating is controlled between 5-9 um.

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