Placement accuracy

Wolf et al. introduced the self-assembly, transfer, and integration (S ATI) of nanoparticles with high placement accuracy.86 87 Silica and polymer nanoparticles were positioned on a PDMS stamp through convective assembly (Fig. 13.14). By controlling the printing temperature or by using a thin polymer layer as an adhesion layer, nanoparticles of different shapes and sizes were printed onto the target substrate. 

Drop placement accuracy Exact drop landing position is uncertain, due to various parameters such as jet-to-jet variations, single jet-overtime, sensitivity to nozzle straightness, nozzle and surface wetting, nozzle plate contamination, ink formulation and condition, and drop velocity. This issue is worse for longer flight paths or "throw distance". 

Fig. 14. Optical micrograph of a printed transistor showing large overlap between gate and source/drain. This overlap is necessary to account for large variability in drop placement accuracy...

The real problems with surface mounting are to cope with the placement accuracies and inspection, and as such do not involve the substrate. 

The spacer double-patterning approach has some issues, the main one of which concerns placement accuracy of the features, which requires excellent dose and etch uniformity control. Equally problematic is the fact that the spacers may not stay in place at the proper location after the material to which they are attached (the HM pattern) is removed. Forming acceptable uniform spacer profiles that will yield uniform CDs is not a trivial exercise. In addition, the etch pattern transfer steps, often involving delicate removal of materials adjacent to the spacers, place unusually tight etch process tolerance on this technique, in order to have a successful outcome. 

The average placement accuracy achieved in this these tests is 10 pm which is close to the accuracy limitations imposed by the motion and alignment systems of the printing platform used. 

The trend in component packaging towards miniaturization of standard components and the development of new packages for components with high pin account (fine pitch, /rBGA, flip-chip) are increasing requirements for placement accuracy. 

One way for SMD assembly onto MID is to use six-axis robots, which arc designed as geometry-flexible handling systems for reaching each point in the workspace with every possible orientation of the tool. The available placement systems for SMD assembly onto PCBs are optimized for placement accuracy and speed. In order to work with these systems on MIDs, it is important to be able to move them during the process (Feldmann and Krimi 1998). 

Assembly of silicon chips onto substrates with anisotropically conductive adhesives uses specialized equipment, initially developed for ffip-chip solder and TAB inner lead bonding. Heat and pressure are transmitted to the adhesive through a thermode attached to a robotic arm or a high-precision linear translator. Equipment requirements are more demanding than for solder assembly, as no self-alignment can occur. A minimum placement accuracy of 0.0005 in. is required. Coplanarity between the substrate and die is critical one study reports maintaining coplanarity to within 0.00004 in. [19]. The pressure required to achieve interconnection depends on the size of the die, the type of conductive particle used, and the viscosity of the adhesive at the bonding temperature. 

Model/Supplier Board Sizes (in X in) Throughput (placements/hr) Placement Accuracy Part Types Placed... 

Lay-down rates substantially higher than. hand lay up, with improved placement accuracy and reduced human error. 

Brown CG, et al. Placement accuracy of percutaneous transthoracic pacemakers. Am J Emerg Med 1985 3 193. 

Burbank F, Forcier N (1997) Tissue marking clip for stereotactic breast biopsy initial placement accuracy, long term stability and usefulness as a guide for wire localization. Radiology 205 407-415... 

A more recent application for formulations containing tiie aqueous developed conductors is the production of displays such as plasma high-definition television panels. The line resolution and placement accuracy of the photocurable pastes in this application can be used to generate more pixels per square xmit of panel, resulting in improved picture quality. 

DCA refers to the assembly of an unpackaged active semiconductor device directly onto the circuit board. The interconnections are made either by wirebonding or by solder bumps on the front side of the die. The latter application is referred to as FC attachment and can be implemented into a surface-mount assembly process as long as existing equipment can accommodate the placement accuracy required for the very small solder bumps and pads. Otherwise, a dedicated cell may be required. 

A step-and-repeat process allows the fabrication of smaller and cheaper stamps and a better control of the placement accuracy [8]. Such a process is easier to implement with a UV system than with a thermal system. 

In general, there is little impact on the com-ponentplacementprocesswhenimplementing a lead-free process. Components will have a lead-free finish, however the shape and size remains the same. One area of concern in the component placement process is placement accuracy. Several studies indicate that components that would center back to the PCB pads in a tin/lead process will not center back as well in a lead-free process. We will have to monitor the placement process to ensure components are placed onto the PCB pads. 

Placement accuracy of less than 100 pm is achieved through substrate alignment at each placement head, using fiducials on the paper. A further optical sensor measures any deviation between foil pitch and index pitch, ensuring accurate positioning of the paper laminate at all times, independently of any stretch in the paper. 

For good practise, the rock should be dropped onto the geotextile filter from a height less than 1.5 m. This ensures good placement accuracy and consistency and ensures limited damage potential to the geotextile filter during rock placement. Subsequent rock and concrete layers in the revetment structure should be placed in the same manner. 

Verein Deutscher Ingenieure (VDI), Verband der Elektrotechnik Elektronik Informationstechnik (VDE) Placement of printed circuit boards determination of placement accuracy and performance of SMD pick place machines. Berlin Beuth-Verlag, 1991. 

There are concerns with lead-free terminated BGA components among them are wetting and self-centering characteristics that impact placement accuracy requirements and manufacturing yields [49]. 

The types of feeders used and size of a component can also influence placement accuracy. Large feeder site tolerances at a component location can result in a deviation between the component center point and the actual pick-up location. The deviation in the theta axis can be exaggerated due to larger component body sizes. As the component body increases, rotational... 

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