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2024年激光直接成像（LDI）设备市场前景分析引言激光直接成像（Laser Direct Imaging，LDI）是一种通过使用激光光源直接将图像转移到PCB（Printed Circuit Board，印刷电路板）上的技术。
随着电子产品的不断发展和更新，LDI技术在PCB制造行业中的应用越来越广泛。
本文将对激光直接成像（LDI）设备市场的前景进行分析。
1. LDI设备市场现状目前，全球LDI设备市场正在快速增长。
随着电子行业对更高性能和更复杂电路板的需求不断增长，传统的光刻技术已经无法满足这些需求。
LDI作为一种非常有效的替代技术，成为了电子制造商的首选。
2. LDI设备市场的驱动因素LDI设备市场的增长受到多个驱动因素的影响。
首先，随着电子设备的微型化和多功能化，印刷电路板上的线路和元器件变得越来越紧凑，要求更高的精度和分辨率。
LDI技术可以提供比传统光刻技术更高的分辨率和精度，满足现代电子产品的要求。
其次，传统的光刻技术需要使用光罩，而LDI技术不需要光罩制造，因此可以节省制造成本和时间。
这使得LDI技术对制造商更加吸引，提高了LDI设备市场的需求。
另外，LDI技术具有更好的灵活性和适应性。
它可以在几乎任何类型的基板上进行图像转移，包括薄膜和曲面基板。
这使得LDI设备市场的应用范围更广，满足了不同制造需求的需求。
3. LDI设备市场的发展趋势未来几年，LDI设备市场有望保持强劲增长。
首先，随着新一代电子产品的不断涌现，对高性能和高精度PCB的需求将继续增长，这将推动LDI设备市场的发展。
其次，随着人们对可持续发展和环保的关注，传统光刻技术所产生的废液和废气问题成为了制造商关注的焦点。
LDI技术可以减少或消除这些废物的产生，因此更环保。
这将使得LDI设备市场在环保产业中的地位提升。
另外，LDI技术的研发和创新也将推动市场的发展。
目前，研究人员正在努力改进LDI设备的分辨率、速度和精度，以满足不断提高的要求。
光绘机的概念光绘机又叫做激光光绘机，是一种集激光光学技术、微电子技术和超精密机械于一体的的照排产品，用于在感光菲林胶片上绘制各种图形，图像，文字或符号。
PCB光绘机图激光光绘机原理激光光绘机的原理其实是很简单的，因为激光光绘机是用是用激光对菲林进行扫描产生图形的，其原理正如电视机显像管中电子枪扫描屏幕上的荧光物质一样。
首先，将印制电路板的图面映像到一个大存储阵列中，然后使激光束按照存储阵列中相应单元的值被打开或关闭(调制)，从而得到所需要的工艺菲林。
激光光绘机采用激光做光源，有容易聚焦、能量集中等优点，对瞬间快速的底片曝光非常有利，绘制的底片边缘整齐、反差大、不虚光。
曝光采用扫描式，无论密度多大，均能在最短时间内完成曝光，绘制一张底片只需几分钟。
因此成为当今光绘行业的主流。
激光光绘机的光源多采用气体激光器，如氩、氦和氖等。
气体激光器的光源强度大但寿命却有限，约6000～10000h，因此使用一年多就需要更换光源。
现在一些光绘机生产厂家采用了半导体激光器作为光源，但较大功率的半导体激光器的生产还不很成熟。
现在激光光绘机因为原理简单，操作方便，被应用在了各行各业上，其中当然也包括PCB行业，在印刷线路板行业使用的光绘机我们把他叫做PCB光绘机。
PCB光绘操作的介绍PCB光绘操作的步骤不能说简单，也谈不上复杂，下面我们就一起来谈论一下关于PCB光绘的操作流程。
激光光绘系统由主控计算机、图形处理卡、激光光绘机和软件组成。
它是对计算机图像、文字和数据等信息进行处理，最终由激光光绘机输出制版菲林，属于计算机辅助制版系统。
根据系统配置的软件不同，它可以制作PCB光绘菲林、标牌面板菲林、丝网印刷菲林和彩色胶印分色菲林等多种菲林底版。
流程如下图所示：（PCB/LCD设计图）-->（CAM系统）-->（Gerber 文件） -->（光绘软件）-->（光栅图像处理器（RIP））-->（激光光绘机） -->（菲林冲片机）-->（菲林）在PCB光绘的时候，我们要做好很多的准备，其中包括软件的使用，软件使用时注意以下几点：光绘软件使用过程中，注意光绘文件的有序保存，最好不要将Gerber文件、光栅文件、临时文件等非程序文件置于软件安装目录中，以免删除时误删掉程序文件，破坏软件的运行。
PCB制作过程中激光直接成像的三种方式激光直接成像让pcb制作工艺过程简化了至少60%，而传统的底片图片转移却需要十几个步骤。
那么PCB制作过程中激光直接成像都有哪些方式呢？全世界的pcb制作商所配备的LDI设备都属于UV光的LDI，按其工艺可以具体分为三种：1）光致抗蚀剂的激光直接成像。
这一类型是指对涂覆有专用光致抗蚀剂的在制板进行激光直接成像。
在制板上要完成导电图形基于如下三个步骤：第一步：利于LDI在激光直接在制板上的专用光致抗蚀剂进行感光。
激光感光是由cad图形数据或计算机已存储的图形数据进行控制激光扫描的，而专业光致抗蚀剂的光敏性要比传统的光致抗蚀剂光敏要强得多（约10倍）来进行激光扫描，才能取得高的PCB图形转移的生产率。
第二步：化学显影。
专用光致抗蚀剂仍采用传统的弱碱性碳酸钠溶液进行显影。
第三步：化学蚀刻。
由于专用的光致抗蚀剂是属于耐酸性（或则耐酸性强于耐碱性）的，因此要采用酸性氯化铜蚀刻溶液等来进行蚀刻。
2）pcb制作采用化学镀锡的激光直接成像。
在制板上化学镀锡的激光直接成像（LDI),某些文献又称为激光直接刻板。
这一类型是指在制板上利用化学方法镀上一层很薄的抗蚀层锡，然后利用激光蚀刻去不需抗蚀刻、保护的锡层及底下的部分厚度（3μm~5μm)的铜箔，然后进行化学蚀刻。
由于锡层在0.5μm~1.0μm厚度）是抗碱不耐酸的。
3）以覆铜箔的在制板上的激光直接成像，这一类型是指仅在覆铜箔在制板上的激光直接成像。
他不需要对在制板进行任何涂覆抗蚀保护层，而是直接利用激光蚀刻去不需要的铜箔，但是为了损伤介质厚度，往往还留下3μm~5μm厚度的铜箔，然后进行严格控制的快速化学蚀刻而出去留下的铜箔厚度。
因此在制板上的铜导体图形的铜厚度将会变薄些。
这具体问题具体分析。
综上所述我们了解到了PCB生产制作过程中使用的激光直接成像的类型方式，工艺在于精益求精，不断实践和优化提升。
深圳金瑞欣特种电路是专业的电路板打样和中小批量生产厂家，主营2-30层高多层板，、高频板、厚铜板、Hdi板等。
丝网印刷直接制版（CTS）激光成像技术及设备激光技术介绍激光技术（见图1）的输出方式是由激光头产生光柱并进行曝光，曝光过程中把网版直接当作胶片。
激光曝光与喷墨制版的区别是激光成像使用激光而非油墨，从材料而言，即便宜又环保。
但激光曝光系统有一问题是需要专用感光胶，因为激光曝光的波段只有较窄的几个毫微米，曝光范围小，与感光范围在360nm～420mm内的传统感光胶的不匹配，所以只能使用专用感光胶。
这种系统在间接制网印版的工艺方面用的较多。
图2是激光曝光成像的主要技术环节。
图1 激光成像系统文 杨芳图2 Screen Setter成像系统（注：Reflector：反射镜；UV-lamp：UV灯；optical lens：光学镜头；DMD：数字微镜设备；Lens：镜头；stencil：网版。
）在激光成像制版中，也有人提出在非图文部分直接喷射感光胶再固化的方法，理由是这样就不需显影处理。
但是考虑到感光胶粘度、流动性、丝网网孔大小不同等因素，这种方法在实际操作中实用性不高，所以较少人去研究这种方法。
激光曝光系统除了CTS系统有的优点外，它的缺点就是对感光胶的使用要求比较严格。
这种技术最适用于每天重复使用同一种油墨在同一种介质上印刷的工作者。
Stencil Writer系统Stencil Writer系统由Berg Engneering公司生产，在1997年投入使用，它的应用主要集中于工业精细印刷和商业印刷。
此系统采用氩激光直接曝光成像，用于间接的丝印制版工艺（即先在感光片上形成镂空的图像，然后进行贴网的制版工艺）。
该系统配备了一款名为“Custom dot”的软件，能影印高质量、连续调的图像。
系统允许接受PC格式、MAC格式和Postscript level格式文件。
系统可达分辨率和速度分别为1270dpi和50%网点覆盖率10min 制1m2。
瑞士Safer公司提供的Safer LDS由于使用材料的恒定性，这种系统最受DVD 以及CD制造商的欢迎。
印刷制版中的激光技术应用的原理激光技术在印刷制版中的应用原理主要包括激光光束的形成、激光光束的调制和激光光束的投射。
激光光束的形成是通过激光器产生的。
激光器通常由激光介质、泵浦源和光学谐振腔组成。
激光介质的种类有很多，如气体、液体或固体等。
当激光介质处于激发态时，外界的泵浦源（如电流、光、化学反应等）可以使其处于受激辐射的状态，进而激发介质分子向较低能级跃迁。
这种辐射过程是自发辐射和受激辐射的综合效果，它产生了具有高能量、高亮度和高方向性的激光光束。
光学谐振腔是一个能够反射激光光线的结构，它可以反射光线，并将它们反复通过激光介质，从而提高激光光束的放大程度。
最终，通过一系列的过程，激光器可以产生高功率的激光光束。
激光光束的调制是为了满足印刷制版的要求。
调制一般包括功率调制和空间调制。
功率调制是通过改变输入光束的功率来实现的，可以通过控制激光的泵浦源或激发介质的参数来调节，以获得所需的功率输出。
空间调制是指通过空间光调制器（如光栅、液晶等）改变激光光束的相位和振幅来实现，以进一步调试光束的特性。
这样可以将光束聚焦到一个确定的位置，以便在制版过程中更好地控制激光的能量分布。
激光光束的投射是通过合适的光学系统来实现的，以便将光束准确地投射到印刷制版的目标上。
投射一般需要满足激光光束的均匀性、稳定性和焦距等要求，以确保最终的印刷质量。
激光光束的均匀性通过调节光束形状（如圆形、方形等）和能量分布来实现。
光束的稳定性通过合理设计和调节光学系统的参数来实现。
焦距的调节是基于制版材料的类型和厚度来实现的，以实现所需的刻印或曝光效果。
除了激光技术在印刷制版中的基本原理外，还有一些与激光技术相关的辅助技术也在印刷制版中得到了应用。
例如，激光束的散斑技术可以通过调整激光光源和光学系统来消除激光光束的散斑效应，从而获得更好的印刷效果。
激光束的光谱分析和调控技术可以用于实时监测激光光束的性能，并根据需求进行调节，以获得更好的印刷质量。
PCB全制作流程中的激光直接成像技术应用Graph 1: trend of line & space at DYCONEX over the last 10 years The consequent use of LDI capability over the complete PCB manufacturing flowDaniel Schulze, Uwe KramerDYCONEX AGGrindelstrasse 408303 Bassersdorf, SwitzerlandT3.4 PCB QualityOral PresentationAbstractThe systematic implementation of optimized LDI (Laser Direct Imaging) photo resist types, LDI exposure units and fine line AOI (Automated Optical Inspection) equipment enhances the production technology and provides optimized PCB solutions for customers. This standardization results in a significantly faster and easier process flow with very precise registration. For high-reliability medical implants, full traceability can be obtained by adding individual serial numbers, date stamps and 2D barcodes for recording various process parameters.Design requirementsDriven by the assembly technology and analyzing the design requirements of the customers over the last 10 years a clear trend to smaller feature sizes is seen. A typical medical implantable product has afeature size of 50 μm line /space. Typical via diametersbetween 50 and 75 μm andpad sizes between 150 μm and 250 μm are standard tofind on these markets. Toassemble resistors of 0201packagingsizes will increase the requirements to the solder maskalignment as well down to25 μm alignment precision.During the quotation phase a detailed design rule check (DRC) has to be done to analyze customers design requirements. Dependent on these requirements like annular ring, layer to layer accuracy or solder mask to artwork accuracy the right registration systems have to be chosen to define the most cost effective and precise manufacturing flow.The graph below shows that the corresponding alignment accuracies are dependant on the customer design and finally used registration concept within the PCB manufacturing.Graph 3: registration concept dependant on customer design class using the annular ring as exampleGraph 2: typical misalignment failure modes Registration SystemsLaser via LDI Artwork Solder maskMechanical via LDI Artwork Solder maskPlasma via LDI Artwork Solder maskaverage compensationstep & repeat compensationaverage compensationindividual compensationindividual compensationindividual compensationindividual compensationaverage compensationaverage compensationaverage compensationaverage compensationEquipment requirementsThe challenge for PCB manufacturers is to constantly implement new manufacturing technologies to satisfy the customers growing demand in PCB complexity, cost efficiency and shorter delivery cycle times. In addition these requirements from the customers have to be linked to profitability of the supplier. Oneof the trends which has been observedduring the last years is the direct imagingtechnology. The growing market for directimaging tools reflects the increasingvariety of DI (Direct Imaging)technologies and vendors. Specializedsystems for different requirements are available. There are entry level systems,tools with double stage loading for faster throughput, high resolution systems and systems which cope with imaging of solder mask. All these systems offer a great variety of advantages over conventional film exposure which will be described in detail in the next chapters. Before starting with DI technology in production one needs to think about the specifications for the equipment. What should the tools be used for? What is the conversion strategy from film imaging to DI? Are there restrictions from customers which need to be addressed? Should and can the equipment operate in automated mode withoutoperator support? What advantages in detail are of interest for the production environment?Due to the demands of customers the requirements on DI systems are well defined. A film plotter has a resolution of 2.5 μm pixel size in comparison to a modern LDI with coherent light and 1 μm pixel size. Therefore LD I systems can offer resolutions higher than 20 μm line and space. Further requirements of the LDI equipment are registration performance better than 10 μm and programmable compensation schemes to include individual compensation together with step & repeat compensation. Furthermore, the systems need to be able to expose solder masks within a competitive process time. Customers are asking for full traceability during PCB manufacturing. Therefore, implementation of individual serial numbers, bar codes or date stamps during imaging is an important feature.After having defined all these prerequisites the process environment needs to be evaluated for matching the DI properties. Contrary to standard film foil exposure units most LDI systems use only one wavelength. Whenstarting with LDI processing inproduction photo resists are typicallynot optimized for direct imaging. Thismeans they either require longerexposure times compared to filmfoil Graph 4: film exposure and LDI exposure equipmentGraph 5: conventional exposure vs. LDI exposureexposure or they are not suitable at all for DI. Even if the standard photo resist can be exposed with DI the change to LDI optimized resists should be taken into account. Today there is a very big variety of optimized DI resists available on the market.After implementing these resists the cycle time for artwork imaging in comparison to film imaging is significantly reduced.Compared to photo resists conventional solder mask exposure requires much higher exposure energy; up to 800mJ/cm2. When establishing direct imaging processes in manufacturing this fact needs to be taken into account. Depending on other requirements the DI capacity needs to be calculated to be sufficient for conventional solder mask exposure. Optimized direct imaging tools are available on the market which combines both the advantages of direct imaging and the high exposure energy. The other option is to qualify new solder mask materials which are optimized for DI. As mentioned above the need for direct imaging of solder masks is usually given on very thin flex products. However, only a limited number of flexible solder masks are available. These solder masks can be exposed with less than 100mJ/cm2. Since medical customers can not change solder mask during the life cycle of a certified product a qualification of a solder mask for direct imaging is a long-term and strategic decision. Therefore at DYCONEX we have qualified two types of flex solder mask for direct imaging. When applying the solder mask optimized for direct imaging an exposure cycle time of less than 90 seconds per panel is achieved. In comparison to LDI solder mask, conventional solder mask exposure takes 6 times longer.Registration ConceptsSubstrate materials are changing in size during the various manufacturing steps. For example plating, desmearing or any process steps where heat is applied. Therefore a start compensation value is given to the substrates to accommodate for the shrinkage or expansion. Changing the single step artworkexposure to LDI has an influence on the rest of the manufacturing process steps. Conventional film foil exposure with just one single compensation value for the entire manufacturing lot as opposed to single panel compensation value to each individual panel using LDI. Thus the complete registration chain from the beginning of the first drilling step through to the artwork and solder mask exposure and ending up with the final routing has to be reviewed.One of the conventional registration concepts is to build sequential products and align layer to layer referring directly to the inner layer structure. A newer registration system uses x-ray drilling to reference to one or more inner layers at simultaneously. Changing from conventional multilayer registration concept to LDI offers several advantages: less process steps, faster through put time and higher alignment precision.The lower number of process steps in the work flow for LDI registration system is seen in Graph 6. For the conventional registration the reference system needs to be protected with 4stickers prior to plating. The punching of the reference system needs to be done. After that the compensation needs to be measured and the films need to be plotted. During exposure the film needs to be aligned to the panel and for good imaging performance vacuum needs to be applied. If required additional sets of films need to be plotted where compensation deviations within the work order occur. The exposure process itself is typically performed simultaneously on front and back of the panel. The overall process time including the supporting processes is 5 - 10 minutes per panel.For the LDI registration process the reference system can bedrilled and does not need to be protected. No film needs to be plotted and the individual compensation does not need to be measured in advance. The exposure of front and back is done sequentially. The overall process time including application of resist is less than 2 minutes per panel.Graph 6: comparison between conventional registration and LDI registration systemCompensation conceptsBasically within the film exposure process only an average compensation for the entire lot of multiple panels is possible. Depending on the LDI equipment used a variety of different compensation schemes can be applied:average compensationindividual panel compensationstep & repeat compensation (sub panel scaling)Step & repeat scaling can help when highcompensation offsets are present within a workorder. Individual compensation is not feasibledue to the following processes where onlyaverage compensation, like final mechanicalrouting or screen printing has been applied.The most accurate and at the same time mostcomplex scaling concept is the step and repeatregistration and compensation.Comparisons between different compensationschemes show the performance improvements.Very thin flex material tends to non linear distortions which occur through the entire manufacturing process. These distortions can not be compensated completely. All remaining distortions which can not be corrected are reflected in loss ofannular ring and misregistration. Together with the increasing complexity as mentioned in the beginning of this paper the annular ring requirements are also increasing. Today standard alignment requir ements are 25 μm for both artwork and solder mask. Typically thin flex material distortions within a workorder can be higher than 300 ppm. This can result, depending on panel size in more than 50 μm loss in annular ring.When film foil exposure is applied no kind of deviation can be corrected. When using individual panel scaling the panel to panel variation can be compensated. This reduces the amount of annular ring failures by a factor of two. The impact of the non linear distortions can Graph 8: material distortion within one single panelGraph 7: material distortion within a work order of multiple production panelsbe reduced when step & repeat registration is applied. Measurements on 25 μm flex material show that the registration within one workorder is improved again by a factor of two. The conclusion of this is that only DI systems can guarantee the high yields to satisfy increasing demands on high density PCB’s.When individual or step & repeat compensation is applied the same compensation methods should be applied to the following process steps. As an example the artwork and solder mask on a 25 μm thin flex panel is imaged using step & repeat compensation. This results in 25 μm registration accuracy. Nevertheless the distortions within a panel are higher than this. Therefore the final mechanical routing also has to be done with step & repeat compensation. Otherwise positioning failure of the PCB structures relative to the routing contour will occur. In other words, the full potential of individual or step & repeatcompensation needs to be considered for the entire process chain.Individual and step & repeat compensations in artwork imaging are well established in the PCB industry already. Same holds true for laser processing. Last but not least the solder mask imaging is the process which also needs to be converted to direct imaging.average compensation = x panel individual compensation = 1 panelS&R compensation = 1/x panelaverage compensation individual compensationS&R compensation Graph 10: registration performance depend on used registration conceptTraceability InformationAs mentioned above most customers ask for traceability of their products through the entire manufacturing process. Traceability means a unique numbering of the manufacturing lot, panel, delivery panel and print at least. This can mean bar codes and date stamp of customer specific counters. Since for DI process no film needs to be plotted, these features can be implemented directly during exposure. The individual features are etched in copper. The same can be done when solder mask is exposed with direct imaging. On some products a legend print is included. Even here the individual serial number can be exposed. At DYCONEX all artwork exposures enable individual serial numbers for full traceability.Graph 11: Traceability information with LDI exposure and copper etchedConclusionTo achieve higher yields and faster trough-put times achange from conventional manufacturing technologies like film exposure to advanced manufacturing processes like laser direct imaging is necessary for high-end, high-reliability flexible PCB’s in the medical, avionics or semiconductor market. T o use LDI exposure in PCB manufacturing requires several equipment updates. Changing the photo chemistry lines and implementing new photo resists or reference systems are just some examples. Following this path results in a new spectrum of smaller and more miniaturized PCB’s with the advantage of better alignment registration, higher accuracy, faster through put time and a better traceability.Manufacturer IDLot NumberPanel NumberPrin t Position NumberDate CodeCustomer Article Number 2D Barcodecopper etchedBiographyMr. Daniel Schulze studied at the Technical University of Dresden and has a diploma degree in Electrical Engineering. During his diploma thesis and an internship at the Georgia Tech Packaging Research Center he got involved with the work on optical waveguides embedded in PCB’s. In 2005 he started to work as Product Engineer at DYCONEX. Since 2008 he is Engineering Manager at DYCONEX and responsible for the product development of medical imaging PCB’s, hearing aids and cochlear implants, industrial and HF products.Mr. Uwe Kramer studied at the University of Halle/Wittenberg and the Technical University Dresden. He holdsa diploma degree in physics. He is specialized in semiconductor and metal physics. The diploma thesis was done in collaboration with Advanced Micro Devises and Fraunhofer Institute for Mechanics of Materials. Thesis of diploma was three dimensional reconstruction and analysis of grain structure by using fine beam techniques. Mr. Kramer joined DYCONEX in 2008 as process engineer. Since 2013 he is manager of the process module artwork and senior process engineer.。
Graph 1: trend of line & space at DYCONEX over the last 10 years The consequent use of LDI capability over the completePCB manufacturing flowDaniel Schulze, Uwe KramerDYCONEX AGGrindelstrasse 408303 Bassersdorf, SwitzerlandT3.4 PCB QualityOral PresentationAbstractThe systematic implementation of optimized LDI (Laser Direct Imaging) photo resist types, LDI exposure units and fine line AOI (Automated Optical Inspection) equipment enhances the production technology and provides optimized PCB solutions for customers. This standardization results in a significantly faster and easier process flow with very precise registration. For high-reliability medical implants, full traceability can be obtained by adding individual serial numbers, date stamps and 2D barcodes for recording various process parameters.Design requirementsDriven by the assembly technology and analyzing the design requirements of the customers over the last 10 years a clear trend to smaller feature sizes is seen. A typical medical implantable product has afeature size of 50 µm line /space. Typical via diametersbetween 50 and 75 µm andpad sizes between 150 µm and 250 µm are standard tofind on these markets. Toassemble resistors of 0201packagingsizes will increase the requirements to the solder maskalignment as well down to25 µm alignment precision.During the quotation phase a detailed design rule check (DRC) has to be done to analyze customers design requirements. Dependent on these requirements like annular ring, layer to layer accuracy or solder mask to artwork accuracy the right registration systems have to be chosen to define the most cost effective and precise manufacturing flow.The graph below shows that the corresponding alignment accuracies are dependant on the customer design and finally used registration concept within the PCB manufacturing.Graph 3: registration concept dependant on customer design class using the annular ring as exampleGraph 2: typical misalignment failure modes Registration SystemsLaser via LDI Artwork Solder maskMechanical via LDI Artwork Solder maskPlasma via LDI Artwork Solder maskaverage compensationstep & repeat compensationaverage compensationindividual compensationindividual compensationindividual compensationindividual compensationaverage compensationaverage compensationaverage compensationaverage compensationEquipment requirementsThe challenge for PCB manufacturers is to constantly implement new manufacturing technologies to satisfy the customers growing demand in PCB complexity, cost efficiency and shorter delivery cycle times. In addition these requirements from the customers have to be linked to profitability of the supplier. Oneof the trends which has been observedduring the last years is the direct imagingtechnology. The growing market for directimaging tools reflects the increasingvariety of DI (Direct Imaging)technologies and vendors. Specializedsystems for different requirements are available. There are entry level systems,tools with double stage loading for faster throughput, high resolution systems and systems which cope with imaging of solder mask. All these systems offer a great variety of advantages over conventional film exposure which will be described in detail in the next chapters. Before starting with DI technology in production one needs to think about the specifications for the equipment. What should the tools be used for? What is the conversion strategy from film imaging to DI? Are there restrictions from customers which need to be addressed? Should and can the equipment operate in automated mode without operator support? What advantages in detail are of interest for the production environment?Due to the demands of customers the requirements on DI systems are well defined. A film plotter has a resolution of 2.5 µm pixel size in comparison to a modern LDI with coherent light and 1 µm pixel size. Therefore LDI systems can offer resolutions higher than 20 µm line and space. Further requirements of the LDI equipment are registration performance better than 10 µm and programmable compensation schemes to include individual compensation together with step & repeat compensation. Furthermore, the systems need to be able to expose solder masks within a competitive process time. Customers are asking for full traceability during PCB manufacturing. Therefore, implementation of individual serial numbers, bar codes or date stamps during imaging is an important feature.After having defined all these prerequisites the process environment needs to be evaluated for matching the DI properties. Contrary to standard film foil exposure units most LDI systems use only one wavelength. Whenstarting with LDI processing inproduction photo resists are typicallynot optimized for direct imaging. Thismeans they either require longerexposure times compared to filmfoil Graph 4: film exposure and LDI exposure equipmentGraph 5: conventional exposure vs. LDI exposureexposure or they are not suitable at all for DI. Even if the standard photo resist can be exposed with DI the change to LDI optimized resists should be taken into account. Today there is a very big variety of optimized DI resists available on the market. After implementing these resists the cycle time for artwork imaging in comparison to film imaging is significantly reduced.Compared to photo resists conventional solder mask exposure requires much higher exposure energy; up to 800mJ/cm2. When establishing direct imaging processes in manufacturing this fact needs to be taken into account. Depending on other requirements the DI capacity needs to be calculated to be sufficient for conventional solder mask exposure. Optimized direct imaging tools are available on the market which combines both the advantages of direct imaging and the high exposure energy. The other option is to qualify new solder mask materials which are optimized for DI. As mentioned above the need for direct imaging of solder masks is usually given on very thin flex products. However, only a limited number of flexible solder masks are available. These solder masks can be exposed with less than 100mJ/cm2. Since medical customers can not change solder mask during the life cycle of a certified product a qualification of a solder mask for direct imaging is a long-term and strategic decision. Therefore at DYCONEX we have qualified two types of flex solder mask for direct imaging. When applying the solder mask optimized for direct imaging an exposure cycle time of less than 90 seconds per panel is achieved. In comparison to LDI solder mask, conventional solder mask exposure takes 6 times longer.Registration ConceptsSubstrate materials are changing in size during the various manufacturing steps. For example plating, desmearing or any process steps where heat is applied. Therefore a start compensation value is given to the substrates to accommodate for the shrinkage or expansion. Changing the single step artwork exposure to LDI has an influence on the rest of the manufacturing process steps. Conventional film foil exposure with just one single compensation value for the entire manufacturing lot as opposed to single panel compensation value to each individual panel using LDI. Thus the complete registration chain from the beginning of the first drilling step through to the artwork and solder mask exposure and ending up with the final routing has to be reviewed.One of the conventional registration concepts is to build sequential products and align layer to layer referring directly to the inner layer structure. A newer registration system uses x-ray drilling to reference to one or more inner layers at simultaneously. Changing from conventional multilayer registration concept to LDI offers several advantages: less process steps, faster through put time and higher alignment precision.The lower number of process steps in the work flow for LDI registration system is seen in Graph 6. For the conventional registration the reference system needs to be protected with4stickers prior to plating. The punching of the reference system needs to be done. After that the compensation needs to be measured and the films need to be plotted. During exposure the film needs to be aligned to the panel and for good imaging performance vacuum needs to be applied. If required additional sets of films need to be plotted where compensation deviations within the work order occur. The exposure process itself is typically performed simultaneously on front and back of the panel. The overall process time including the supporting processes is 5 - 10 minutes per panel.For the LDI registration process the reference system can be drilled and does not need to be protected. No film needs to be plotted and the individual compensation does not need to be measured in advance. The exposure of front and back is done sequentially. The overall process time including application of resist is less than 2 minutes per panel.Graph 6: comparison between conventional registration and LDI registration systemCompensation conceptsBasically within the film exposure process only an average compensation for the entire lot of multiple panels is possible. Depending on the LDI equipment used a variety of different compensation schemes can be applied:• average compensation• individual panel compensation• step & repeat compensation (sub panel scaling)Step & repeat scaling can help when highcompensation offsets are present within a workorder. Individual compensation is not feasibledue to the following processes where onlyaverage compensation, like final mechanicalrouting or screen printing has been applied.The most accurate and at the same time mostcomplex scaling concept is the step and repeatregistration and compensation.Comparisons between different compensationschemes show the performance improvements.Very thin flex material tends to non linear distortions which occur through the entire manufacturing process. These distortions can not be compensated completely. All remaining distortions which can not be corrected are reflected in loss of annular ring and misregistration. Together with the increasing complexity as mentioned in the beginning of this paper the annular ring requirements are also increasing. Today standard alignment requirements are 25 µm for both artwork and solder mask. Typically thin flex material distortions within a workorder can be higher than 300 ppm. This can result, depending on panel size in more than 50 µm loss in annular ring.When film foil exposure is applied no kind of deviation can be corrected. When using individual panel scaling the panel to panel variation can be compensated. This reduces theamount of annular ring failures by a factor of two. The impact of the non linear distortions can Graph 8: material distortion within one single panelGraph 7: material distortion within a work order of multiple production panelsbe reduced when step & repeat registration is applied. Measurements on 25 µm flex material show that the registration within one workorder is improved again by a factor of two. The conclusion of this is that only DI systems can guarantee the high yields to satisfy increasing demands on high density PCB’s.When individual or step & repeat compensation is applied the same compensation methods should be applied to the following process steps. As an example the artwork and solder mask on a 25 µm thin flex panel is imaged using step & repeat compensation. This results in 25 µm registration accuracy. Nevertheless the distortions within a panel are higher than this. Therefore the final mechanical routing also has to be done with step & repeat compensation. Otherwise positioning failure of the PCB structures relative to the routing contour will occur. In other words, the full potential of individual or step & repeat compensation needs to be considered for the entire process chain.Individual and step & repeat compensations in artwork imaging are well established in the PCB industry already. Same holds true for laser processing. Last but not least the solder mask imaging is the process which also needs to be converted to direct imaging.average compensation = x panel individual compensation = 1 panelS&R compensation = 1/x panelaverage compensation individual compensationS&R compensation Graph 10: registration performance depend on used registration conceptTraceability InformationAs mentioned above most customers ask for traceability of their products through the entire manufacturing process. Traceability means a unique numbering of the manufacturing lot, panel, delivery panel and print at least. This can mean bar codes and date stamp of customer specific counters. Since for DI process no film needs to be plotted, these features can be implemented directly during exposure. The individual features are etched in copper. The same can be done when solder mask is exposed with direct imaging. On some products a legend print is included. Even here the individual serial number can be exposed. At DYCONEX all artwork exposures enable individual serial numbers for full traceability.Graph 11: Traceability information with LDI exposure and copper etchedConclusionTo achieve higher yields and faster trough-put times a change from conventional manufacturing technologies like film exposure to advanced manufacturing processes like laser direct imaging is necessary for high-end, high-reliability flexible PCB’s in the medical, avionics or semiconductor market. To use LDI exposure in PCB manufacturing requires several equipment updates. Changing the photo chemistry lines and implementing new photo resists or reference systems are just some examples. Following this path results in a new spectrum of smaller and more miniaturized PCB’s with the advantage of better alignment registration, higher accuracy, faster through put time and a better traceability.Manufacturer IDLot NumberPanel NumberPrin t Position NumberDate CodeCustomer Article Number 2D Barcodecopper etchedBiographyMr. Daniel Schulze studied at the Technical University of Dresden and has a diploma degree in Electrical Engineering. During his diploma thesis and an internship at the Georgia Tech Packaging Research Center he got involved with the work on optical waveguides embedded in PCB’s. In 2005 he started to work as Product Engineer at DYCONEX. Since 2008 he is Engineering Manager at DYCONEX and responsible for the product development of medical imaging PCB’s, hearing aids and cochlear implants, industrial and HF products.Mr. Uwe Kramer studied at the University of Halle/Wittenberg and the Technical University Dresden. He holds a diploma degree in physics. He is specialized in semiconductor and metal physics. The diploma thesis was done in collaboration with Advanced Micro Devises and Fraunhofer Institute for Mechanics of Materials. Thesis of diploma was three dimensional reconstruction and analysis of grain structure by using fine beam techniques. Mr. Kramer joined DYCONEX in 2008 as process engineer. Since 2013 he is manager of the process module artwork and senior process engineer.。
