The key design of Fiducial Mark 光学定位点的关键设计

Fiducial Marks are a feature of the printed circuit board artwork, created in the same process as the circuit artwork. The circuit pattern and fiducial should be etched at the same step. Fiducial Marks provide common measurable points for all steps in the assembly process. This allows all automated assembly equipment to accurately locate the circuit pattern.

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Fiducial Marks are generally categorized in two types: Global Fiducials,Fiducial marks used to locate the position of all features on an individual.printed circuit board. When multiple boards are processed as a panel, the global fiducials may also be referred to as panel fiducials if used to locate.the circuits from the panel datum. Local Fiducials. Fiducial marks used to locate the position of an individual component that may require more precise location, such as a .020” pitch QFP.

 

Global and/or panel fiducials should ideally be located on a three point grid based systemGlobal fiducials should be located on all PCB layers that contain components to be mounted with automated equipment.

 

Fiducials should have a soldermask opening large enough to provide good contrast and keep the fiducial clear of soldermask to enable accurate identification by all vision alignment systems.A minimum of two global fiducial marks is needed for correction of translational offsets (x and y position) and rotational offsets (theta position). These should be located diagonally opposed and as far apart as possible on the circuit or panel.

 

Fiducial contain: Shape: The optimal fiducial mark is a solid filled circle.The minimum diameter of the fiducial mark should be 1mm (0.040 in). The maximum diameter of the fiducial should be 3mm (0.120 in). Fiducial marks on the same PCB should not vary in size by more than 25 microns (0.001 in). Clearance: A clear area devoid of any other circuit features or markings should be maintained around the fiducial mark. The size of the clear area should be equal to the radius of the mark. A preferred clearance around the mark is equal to the mark diameter. Material:The fiducial may be bare copper; bare copper protected by a clear anti-oxidation coating, nickel or tin plated, or solder coated (HASL).The preferred thickness of the plating or solder coating is 5 to 10 microns (0.0002 to 0.0004 in). Solder coating should not exceed 25 microns (0.001 in).If solder mask is used, it should not cover the fiducial or the clearance area.Flatness:The flatness of the surface of the fiducial mark should be within 15 microns (0.0006in).Edge Clearance:The fiducial marks should be located no closer to the PCB edge than the sum of 7.62mm (0.300 in) (SMEMA Standard Transport Clearance) and the minimum fiducial clearance required. Contrast: Most machine vision recognition systems perform best when a consistent high contrast is present between the fiducial mark and the PCB base material.

 

基准点是印制电路板的工艺特点,在同一个进程创建的电路图形。电路图案和基准点应该在同一步中蚀刻。基准点是所有装配过程中常见的测点。这使得所有的要准确定位的自动化装配设备都要用到它。

 

基准标志通常分为两类:整板基准点基准标记用于定位所有的功能在一个单独的位置。印刷电路板。当多个板被处理为面板时整板基准点也可称为面板基准如果用来定位面板数据的电路。局部基准,基准标记用于定位一个单独的组件,可能需要更精确的位置,如0.02间距QFP

 

整板和/或面板基准应该位于一三点的网格系统。全局基准点应位于包含组件被安装自动化设备所有PCB层。

 

基准点应该有一个足够大的阻焊开提供良好的对比度和保持基准摆脱阻焊使所有视觉对准系统的准确识别。最小的两个全球基准标记是平移偏移校正所需的(XY位置)和旋转偏移(θ位置)。在电路或面板上,这些应位于对角方向相反,尽可能地分开

 

基准包含:铜皮:最佳基准标记是一个实体填充圆。基准标记的最小直径应为1mm0.040)。该基准的最大直径应为(0.120)。在基准标记相同的印刷电路板的尺寸不应超过25微米(0.001英寸)。间距:一个明确的区域,没有任何其它电路特征或标记应保持在基准标记。明确面积的大小应与标的半径相等。在标记的一个优选的间隙等于标记直径。材料:基准可能赤裸的铜;赤裸的铜以明显的抗氧化涂层保护,镍或锡电镀,或焊料涂覆(HASL)。的电镀或焊料涂层厚度为5微米至10微米的首选(0.00020.0004)。焊料涂层应不超过25微米(0.001)。如果焊料掩模,它不应该包括基准或净空面积。平整度:对基准标记的表面平整度应在15微米(0.0006in)。边缘间距:基准标记应位于不靠近PCB边缘比7.62mm的总和(0.300)(SMEMA标准运输清关)和最低基准通关所需。对比:大多数的机器视觉识别系统的最佳表现在一贯的高对比度的基准标记和PCB基材之间。