Research on the processability of CO2 laser applied to PCB manufacturing

About the Author:

Wu Junquan: Graduated from a university, currently an engineer in the R&D department of Jinbaize Technology Center.

Summary:

As PCB products tend to be shorter, lighter and thinner and diversified in assembly structures, many PCB manufacturers have introduced laser manufacturing processes to cope with the precision processing of products with complex structures. Carbon dioxide laser is often used for PCB micro-blind hole processing and thin plate cutting processing, in fact, it can also be used to develop precision processing of a variety of materials. In this project, new laser processing technologies such as laser cutting of PTFE sheets and laser-controlled deep milling are proposed by studying the principle of laser line and surface processing and the effect of laser processing of various sheets.

Key words:Laser line surface processing PTFE sheet laser cutting Laser controlled deep groove milling

Abstract:

As the PCB product tending to be short, thin and assembly structures with diversified, many PCB manufacturers introduce laser precision machining to deal with the complex structure product. Carbon dioxide laser is used in micro-blind hole machining and sheet cutting. In fact, it can also be used in a variety of materials developing precision machining. By studying the laser line and surface processing principle and the effect of various laser processing, we proposed new laser machining technology such as PTFE material laser cutting, laser depth control milling groove technology and so on.

Key words: Laser Line And Surface Machining; PTFE Material Laser Cutting; Laser Depth Control Milling Groove

1 Introduction

With the rapid development of Electronic technology, many PCB products with complex structures and precise processing have gradually appeared on the market. The requirements of new products for processing accuracy are increasing, and the requirements for product appearance have become stricter, and there is also a demand for using new type of plate to make plates, which makes it difficult for traditional mechanical processing to meet such novel market needs. Since laser processing has superior precision, high-speed processing, and low-cost processing properties that are superior to traditional mechanical processing, more and more manufacturers have begun to introduce laser equipment to develop new plate-making processes to cope with this situation. In order to better develop the CO2 laser processing technology, we first analyze the possible processing modes of the CO2 laser.

2 Analysis of CO2 laser processing mode

The carbon dioxide laser used for PCB processing is usually a high-power pulse shaping laser with a wavelength of 10.6um, which has extremely strong processing capabilities for non-metallic materials. At present, the commonly used carbon dioxide laser processing technologies include micro-blind hole processing, soft board PI cutting, and laser marking, as shown in Figure 1 and Figure 2 below.

图1 激光加工微盲孔                            图2  激光加工PI覆盖膜

可见目前的二氧化碳激光加工特点在于点加工和简单的薄板线加工，这不禁让我们开始思考二氧化碳激光是否具有其它加工模式。如何进一步拓展其应用，实现由点及线的线加工方式，以及由点及面的面加工方式，已成为业界同行共同思考的话题。

2.1  二氧化碳激光线加工原理及分析

二氧化碳激光线加工，其实质是由点连成线的点阵式加工。当连成线的相邻光点间距足够小的时候，激光将呈现出平滑的线加工效果，沿线方向激光线加工的效果如下图3所示。

Figure 3 Laser line processing effect along the line

In addition, the processing focal length of the laser has a certain range, and the laser processing energy will attenuate as the processing depth increases. The processing essence is similar to the shape of the V-CUT. However, due to the small diameter of the laser beam and the small openings processed, it is generally considered to have a straight cutting effect, and the line processing effect of the cross section is shown in Figure 4 below.

图4 激光线加工截面效果

2.2  二氧化碳激光面加工原理及分析

激光面加工涉及三个维度，加工时以点阵图形确定加工面的两个维度，以激光能量确定加工深度一个维度。点阵图的设计根据光束径尺寸进行间距计算，铺满整个加工面，可满足激光在各种深度下加工出均匀的平面，如下图5所示。

图5 激光面加工点阵图模型                   图6  激光面加工截面示意图

       以点阵方式进行面加工，加工面的底部会存在微坑，但只要激光能量调整适当，可使得加工深度的可控性不受微坑影响，而且从宏观看加工面几乎是平整的，其加工示意图如上图6所示。

3  二氧化碳激光线面加工模式应用与技术开发

3.1  二氧化碳激光线加工应用研究

3.1.1  PCB材料的激光线加工效果分析

二氧化碳激光通常用于加工非金属材料，非金属材料对二氧化碳激光的能量吸收率较高，因此我们将对环氧树脂+玻纤、PTFE+玻纤及陶瓷填料+玻纤这几类常用的基材进行激光加工效果分析，以研究其激光加工的外观品质及加工可控程度。我们围绕三个方面对多种板材的激光线加工效果进行考察。第一方面是激光加工效率，以同参数下的加工深度比值来表示；第二个方面是加工均匀性，以加工的最大偏差值来表示；第三方面是外观品质，观察加工后的产品外观是否严重碳化。材料的激光线加工效果如下表1所示。

表1  几种材料的激光线加工效果

由上述的激光线加工效果可知，加工效率方面PTFE+玻纤材料的线加工深度比较高，更容易被激光加工；均匀性上最大偏差值均小于0.1mm，表明材料的线加工的可控程度可满足常规外形公差；而加工外观环氧树脂+玻纤材料较容易出现碳化现象，陶瓷填料+玻纤材料也会出现轻微的碳化现象，而PTFE+玻纤材料则不存在碳化现象，若对产品外观要求严格把控时，不同材料的碳化情况应引起注意。

3.1.2  二氧化碳激光线加工技术开发

我们常用激光来进行PI覆盖膜、软板薄板的切割加工，激光线工的能力仿佛被定格于薄板及软性材料的切割加工。通过上述材料对激光加工能力的考察，我们知道激光同样也可满足硬材料的切割，而且控深加工能力很强，因此激光线加工可满足的材料切割品种和材料厚度有更大的开发空间。

(1)软硬结合板单面激光揭盖技术

软硬结合板是新型PCB产品的主力军之一，揭盖技术通常使用机械V-CUT工艺。实际上激光也可实现软硬结合板的揭盖加工[1], Based on the powerful deep processing capability of the laser, the required deep processing within a certain range can be obtained by appropriate adjustment of the laser energy, similar to mechanical V-CUT processing, and the processing effect is shown in Figure 7 and Figure 8 below.

Figure 13: Schematic diagram of laser-controlled deep milling groove processing

4 Conclusion

In summary, carbon dioxide laser can be applied to the line and surface processing of a variety of PCB materials. Some new laser processing technologies derived from laser line and surface processing can easily solve some of the problems of traditional manufacturing processes, thereby achieving fine processing of PCBs. In today’s PCB market with many products, the realization of precision processing of products with complex structures has gradually become a technological development trend in pursuit of high value-added PCB product manufacturing. Laser processing technology carries the mission of high-precision processing, constantly challenging the precision processing limits that are difficult to achieve by traditional manufacturing processes, and is expected to become the mainstream processing technology for precision processing of complex structure PCBs in the future.

references

[1] Lin Yingsheng, Lin Qiheng, Wu Junquan, Chen Yutao, Chen Chun, Research on the application of new technology of carbon dioxide laser drilling machine[J].Printed Circuit Information, 2013, 4.