Manufacturing process of super thick copper multilayer PCB

With the rapid development of power communication modules, 4-6OZ conventional thick copper has been difficult to meet its performance requirements, and the demand for super thick copper PCB of 10-12oz and above is getting higher and higher. This article is talking about 12oz super thick copper, a feasibility study was conducted on the production process of the laminate, and the step-by-step controlled deep etching technology + increased lamination technology was used to effectively realize the processing and production of the 12oz super thick copper multilayer printed board and meet the special needs of customers.

 

1. Introduction to super thick copper PCB

With the rapid development of automotive electronics and power communication modules, super-thick copper foil circuit boards of 12oz and above have gradually become a kind of special PCB boards with broad market prospects, and have received more and more attention and attention from manufacturers; at the same time, along with printing With the wide application of printed circuit boards in the electronic field, the functional requirements of equipment are getting higher and higher. The printed circuit boards will not only provide the necessary electrical connections and mechanical support for electronic components but also gradually be given more With additional functions [1], super-thick copper foil printed boards that can integrate power sources, provide large currents and high reliability have gradually become popular products developed by the PCB industry, with broad prospects.

At present, research and development personnel of the same industry in the industry have successfully developed a double-sided printed circuit board with a finished copper thickness of 10oz through the layered method of successive thickening of electroplated copper sinking + multiple solder mask printing assistance. However, there are few reports on the production of super thick copper multilayer printed boards with a finished copper thickness of 12oz and above; this article mainly focuses on the feasibility study of the production process of 12oz super thick copper multilayer printed boards. Thick copper step-by-step controlled deep etching technology + build-up lamination technology, effectively realizing the processing and production of 12oz ultra-thick copper multilayer printed boards.

 

2. Manufacturing process of super thick copper PCB

2.1 Stacked design of thick copper PCB

This board is a four-layer board, the inner and outer copper layers are 12 oz thick, and the minimum line width and line spacing are 20/20mil. The laminated structure is shown in Figure 1:

Laminate structure - Manufacturing process of super thick copper multilayer PCB

Figure 1 Laminated structure diagram

2.2 Analysis of processing difficulties

❶ Super thick copper etching technology (copper foil is super thick, difficult to etch): purchase a special 12OZ copper foil material, adopt positive and negative controlled deep etching technology to achieve the etching of super thick copper circuits.

❷ Super thick copper lamination technology: The technology of single-sided circuit-controlled deep etching followed by vacuum pressing and filling, effectively reduces the difficulty of pressing. At the same time, it assists the pressing of silicone pad + epoxy pad to solve the problem of super thick copper lamination. Technical problems such as white spots and lamination.

❸ The precision control of the two alignments of the same layer of lines: measurement of expansion and contraction after lamination, adjustment of the expansion and contraction compensation of the line; at the same time, the line production uses LDI laser direct imaging to ensure the accuracy of the overlap of the two graphics.

❹ Super thick copper drilling technology: By optimizing the rotation speed, feed speed, retreat speed, drill life, etc., to ensure good drilling quality.

2.3 Process flow (take 4-layer board as an example)

Manufacturing process of super thick copper PCB - Manufacturing process of super thick copper multilayer PCB

Figure 2 Production process

 

2.5 Process processing method

2.5.1 Super thick copper etching technology

Due to the super thick copper foil, there is no 12oz thick copper core board to buy in the industry. If the core board is directly thickened to 12oz, the circuit etching is very difficult, and the etching quality is difficult to guarantee; at the same time, the difficulty of pressing the circuit after one-time molding is also greatly increased. , Facing a larger technical bottleneck.

In order to solve the above problems, in this super thick copper processing, a special 12oz copper foil material was directly purchased during the structural design. The circuit adopts a step-by-step controlled deep etching technology, that is, the copper foil is first etched 1/2 thickness on the backside → pressed to form a thick copper core Board → etching on the front side to obtain the inner layer circuit pattern. Due to the step-by-step etching, the etching difficulty is greatly reduced, and the pressing difficulty is also reduced.

❶ Line file design

Two sets of files are designed for each layer of the circuit. The first reverse file needs to be mirrored to ensure that the circuit is at the same position during the forward/reverse control deep etching, and there will be no misalignment.

❷ Reverse control deep etching of circuit graphics

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Figure 3 The first reverse-controlled deep etching slice of the circuit pattern

❸ Secondary circuit graphics alignment accuracy control

In order to ensure the coincidence of the two lines, the expansion and contraction value should be measured after the first lamination, and the line expansion and contraction compensation should be adjusted; at the same time,

The automatic alignment of LDI laser imaging effectively improves the alignment accuracy. After optimization, the alignment accuracy can be controlled within 25um.

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Figure 4 The second line graphics alignment accuracy slicing effect

❹ Super thick copper etching quality control

In order to improve the etching quality of super thick copper circuits, two methods of alkaline etching and acid etching were used for comparative testing. It has been verified that the burrs of the acid-etched circuits are smaller and the line width accuracy is higher, which can meet the etching requirements of super thick copper. The effect is shown in Table 1.

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Figure 5 Alkaline etching effect diagram

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Figure 6 Acid etching effect diagram

2.5.2 Super thick copper PCB lamination technology

With the advantages of step-by-step controlled deep etching, although the difficulty of lamination has been greatly reduced, if the conventional method is used for lamination, it still faces many problems, and it is easy to produce hidden quality problems such as lamination white spots and lamination delamination. For this reason, after the process comparison test, the use of silicone pad pressing can reduce laminating white spots, but the board surface is uneven with the pattern distribution, which affects the appearance and film quality; if the epoxy pad is also assisted, the pressing quality is significantly improved. Can meet the pressing requirements of super thick copper.

❶ Super thick copper lamination method

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Figure 7 The surface effect of different pressing methods of super thick copper

❷ Super thick copper laminate quality

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Figure 8 Super thick copper lamination effect slice diagram

Judging from the condition of laminated slices, the line is filled with full, no micro-slit bubbles, and the entire deep-etched part is deeply rooted in the resin; at the same time, due to the problem of super thick copper side etching, the top line width is more than the narrowest line width in the middle part At about 20um, this shape resembles an “inverted ladder”, which will further enhance the grip of the pressing, which is a surprise.

❷ Super thick copper build-up technology

Using the above-mentioned step-by-step controlled deep etching technology + lamination process, layers can be added successively to realize the processing and production of a super thick copper PCB at the same time, when the outer layer is made, the copper thickness is only about 6oz, in the range of conventional solder mask process capability, greatly reduces the process difficulty of solder mask production and shortens the cycle of solder mask production.

 2.5.3 Super thick copper drilling parameters

The thickness of the finished plate after total pressing is 3.0mm, and the overall copper thickness reaches 160um, so there is a certain degree of difficulty in drilling and processing. In order to ensure the quality of the drilling, the drilling parameters were specially adjusted locally. After optimization, the slice analysis showed that the drilling has no defects such as nail heads and thick holes, and the effect is good.

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Figure 9 Super thick copper drilling effect

2.5.4 The effect of super thick copper PCBs

super thick copper PCB - Manufacturing process of super thick copper multilayer PCB

Figure 10 Finished effect diagram of super thick copper printed board

2.5.5 Finished product reliability test

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Figure 11 6 slices of lead-free reflow soldering

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Figure 12 288℃/10S/3 times immersion tin slices

2.5 summary

Through the process of research and development of the super thick copper multilayer printed board, the positive and negative controlled deep etching technology is adopted, and the silicone pad + epoxy pad is used to improve the quality of the lamination during lamination, which effectively solves the difficulty of etching the super thick copper circuit. Common technical problems in the industry, such as super thick laminate white spots and solder masks requiring multiple printing, have successfully realized the processing and production of a super thick copper multilayer printed boards; its performance has been verified to be reliable, which satisfies customers’ Special demand for current.

 

3. Summary

This article provides a processing method for super thick copper multilayer printed boards, and through technological innovation and process improvement, it effectively solves the common technical problems in the industry:

❶ Step-by-step control deep etching technology for positive and negative lines: effectively solve the problem of super thick copper line etching;

❷ Positive and negative line alignment accuracy control technology: effectively improve the overlap accuracy of the two graphics;

❸ Super thick copper build-up lamination technology: effectively realizes the processing and production of a super thick copper multilayer printed boards.

 

4 Conclusion

Super thick copper printed boards are widely used in large-scale equipment power control modules due to their over-current conduction performance. Especially with the continuous development of more comprehensive functions, super-thick copper printed boards are bound to face wider Market prospects. This article is just for reference and reference for peers.

 


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