Aperture Separation Research Articles

Study of Print Release Process in Solder Paste Printing

Solder paste printing is central to the mass reflow soldering process for surface mount technology. The miniaturization of components has put an increased demand on the printing process and requires it to successfully print 75 μm-100 μm(3 to 4 mil) wide apertures. The amount of solder paste deposited is a matter of concern. This study presents results from experiments on printing with apertures having circular, rectangular, square and triangular geometries. The ratio of the printed volume to the aperture volume has been used as a definition of print quality. It was observed that acceptable prints were obtained when the ratio of aperture area to the aperture wall area was more than 0.8. A simple analytical model is also presented for the release of solder paste as the stencil separates from the substrate board assuming that the apertures were filled. The solder is currently treated as a single phase material with Newtonian behavior. The motion of solder paste in the stencil aperture is modelled as the developing viscous flow with velocity boundary layers developing along the walls. The shear strength of the paste is used to determine the area sticking to the wall, thus making it possible to get an estimate of the print quality. The model incorporates the effect of paste properties like viscosity, density, tack and shear strength, and other process variables like aperture dimensions and separation (lift off) velocities between the stencil and the board in predicting the print quality. The model predicts the effect of shear to tack strength of the paste, stencil thickness, and the ratio of aperture to wall area ratio on print quality.

Spatial correlation of Zernike phase-expansion coefficients for atmospheric turbulence with finite outer scale

Aperture-to-aperture correlations of Zernike coefficients associated with atmospheric turbulence with a finite outer scale have been calculated. It is shown that the effect of finite outer scale is to reduce the correlation rapidly for low-order Zernike terms as the aperture separation becomes large. The results can be used to determine the outer scale. We use published data from the Keck telescope to illustrate our method. The results suggest that finite outer scale effects may be important for telescopes in the 8 –10-m class.

RCS characterization of a finite ground plane with perforated apertures: simulations and measurements

The monostatic radar cross section of a finite-size perfectly conducting flat plate with perforated apertures is investigated by simulations and measurements. The geometry of a finite ground plane with triangular apertures resembles airplane and automobile windows. The method of moments surface patch formulation is used to compute the radar cross section of a solid plate, a plate with two widely spaced apertures, and a plate with two closely spaced apertures. The characteristics of the triangular patch mesh can impact the accuracy of the computed results with this formulation. The paper presents a methodology to achieve high quality meshes to ensure that the time and convenience gained by developing the general method of moments code is not lost in mesh construction and convergence tests. The results obtained using the method of moments are compared with results obtained by measurements and physical optics. It is shown that the method of moments simulations and measurements are in good agreement. The key features of the influence of the aperture separation on the RCS patterns are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An upper limit on the aperture separation of ion drift meters

An upper limit has been calculated on the effective aperture separation or detector thickness of ion drift meters of two fundamental types. The limit applies to meters which compare currents collected by detectors with different view directions at the same retarding potential and to meters which measure the entire thermal ion distribution function. For both types, a single scanned detector may be employed instead of multiple detectors, in which case the limit applies to twice the radius of curvature of the path followed by the detector aperture during a scan, (i.e. the diameter of a spinning payload). The limit was found to be important in two cases. First, in the F region on spacecraft with stringent electrostatic cleanliness requirements, the 10% error limit was found to be 40 cm. Second, in the E region, the limit was found to be ≲1 cm.

Acoustic Response of a Circular Receiver to a Circular Source of Different Radius

This Letter considers an approximation for the acoustic response of a circular receiving aperture to a similarly aligned coaxial circular source. Graphical results for the acoustic response versus aperture separation are given for three cases.

Acoustic Response of a Rectangular Receiver to a Rectangular Source

This Letter considers an approximation for the acoustic response of a rectangular receiving aperture to a similarly aligned coaxial rectangular source. Graphical results for the response versus aperture separation are given for two cases.

Diffraction Geometry*

An error-minimizing geometry is deduced for a three-aperture diffraction system. All aperture dimensions and the aperture separation are absolutely determined from initial knowledge of (1) the specimen-detector separation, (2) the diffraction angle, and (3) the tolerable geometric error. Examples of patterns obtained with such optimum systems are compared with typical nonoptimum systems to show the improvement in resolution.