Passive pitches

Acousto-ultrasonics [49] is a guided-wave pitch-catch method. The acousto part in the name reminds one of the reception of guided waves generated by the AE process at a propagating crack. The term ultrasonics infers that this is an active technique in which ultrasonic waves are generated by the transmitter thus this technique is different from the AE technique in that is just a passive technique. 

SMT 2350C/ CELMACS SMT Corp. 2 X 2 to 16 X 20 and 24-79 mils thick Passive device chips 6,200 ICs 1,818 0.04 mm w/IC (vision) head, 0.1 mm w/chip (chucking) head 0402 chips to 1.8 inch (45-mm) square QFP and BGA, fine pitch and non-standard shaped components... 

Cu corrosion after CMP can usually be identified by the rough or mgged Cu surface under SEM as shown in Figure 17.15(d). Cu etching caused by insufficient cleaning or passivation of the Cu fines after CMP is believed to be the root cause of the phenomenon. Such corrosive attack is found to be more severe on smaller Cu areas with a finer pitch [19]. 

Automotive Air Bag Passive automotive restraint consisting of a bag made of flexible material that inflates upon sensing a collision and prevents passengers from pitching forward or from side to side, depending on the type and position of the air bs. ... 

Fig. 7. Polymer LED passive matrix display 160 x 160 pixels with pitch of 300 )am. Picture provided by Nobel Laureate Dr. Alan J. Heeger, courtesy of Uniax Corp., Santa Barbara, Calif...

Printed circuit board (PCB) structures and processes continue to be driven by device miniaturization, functional densification, and speed. The choice of components, actives and passives, and connectors are primary determinants of layer count and layer options, such as copper foil weights. Reductions in chip voltages are matched by an increase in current demand this in turn causes increases in the number and thickness of the plane layers. More device leads combined with decreasing pitch increases the number of vias and interconnecting layers, while miniaturization and weight reduction at the product level forces reduction in the physical package for the product. 

Coarse-pitch surface-mount components, especially passive devices, are affixed to the bottom side of the PWB using surface-mount adhesive. The adhesive is cured prior to wave soldering. The adhesive is in contact with the body of the component, which is aUgned with its respective pads on the circuit board in preparation for wave soldering. 

Many wave designs are available from the various wave-solder machine manufacturers.There are wave machines that provide multiple smaller, turbulent wave(s), which are best for leadless components such as surface-mount passive devices (resistors, capacitors, etc.). Smoother-flowing waves are recommended for components with leads and through holes as well as coarse-pitch surface-mount devices. Wave dynamics are dictated by process values as well as the materials in contact with the wave. As the solder wets to the circuit board materials, solder wetting contact angle and solder viscosity imposes wave peel-off characteristics (see Fig. 47.23). 

Repeatability Limitations. Several studies have documented the low repeatability rate of visual inspection of solder joints. One snch stndy was condncted by AT T at its Federal Systems Division. This study showed that even the same inspector inspecting the same assembly twice had a defect call repeatability rate of only about 50 percent. Two different inspectors inspecting the same assembly had a defect call repeatability rate of only about 28 percent. This study did not include any very-fine-pitch SMT solder joints or 0603 passive components, which are more difficult to inspect visually. 

Automated optical inspection systems also image only a small portion, or view, of the assembly at a time. These systems normally can use somewhat bigger views than the 3-D solder paste systems because the features being extracted often do not require as much magnification as do measurements of solder paste depositions. However, inspection of components, such as 0402, 0201, and 01005 passive components, or very-fme-pitch deposits, can require the same level of magnification and therefore views as small as the 3-D solder paste inspection systems. 

Pre-reflow AOI systems also have the ability to inspect 2-D solder paste however, this ability is utihzed only to inspect a small percentage of the solder paste deposits combined with the component misalignment measurements. Component misalignment measurements cover the passive components, whereas the solder paste measurements cover deposits for BGA, CSP, or fine-pitch QFP devices. Therefore, these systems are placed within production lines after the pick-and-place systems for passive devices but before the pick-and-place systems for the larger area-array and leaded devices. These systems serve the same purpose as those only meant for component placement measurement, both detecting defects and monitoring measurements within control limits to discover process drift as early as possible. 

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