Jun 12, 2003 The resolution of this particular problem became the driving factor behind the design, development, and production of an affordable, innovative and uniquely adaptive tool, the Universal Overhead Top Hat.
Many companies, including DMI International, incorporated the use of specialized arms or holding devices that extend out from the sides of the wave solder pallet in order to reach floating components and hold them in place.
Such adaptations have been proven to work well as long as the problematic components were near the edge of the panel and could be easily reached.
Some of these holding devices were spring loaded; some were custom made to a specific height.
However, both of these "arm" adaptations have inherent limitations and limited success.
The biggest limiting factor in using the "arm" approach to holding down problematic components is the inability to reach them when they are located in the middle of a large PCB.
This is a problem made even more difficult when clear access is blocked by large components along the outside edge of the PCB.
The loss of downward pressure becomes another limiting factor the further away from the anchor point the component is located.
DMI International's Universal Overhead Top Hat overcomes these problems while being adaptable to any manufacturer's fixture.
By using moveable yokes (that attach to the bars with thumb screws in order to hold the top hat in place) the entire width of the circuit board becomes accessible.
Simply loosening the thumbscrews allows repositioning of the yokes to any desired point along the Y-axis.
This attachment method also allows the top hat to be used on any fixture with support bars attached to it.
The slots cut along the length of the top hat allows the operator to position the independent spring plunger housings anywhere along the X-axis.
These two simple adjustments allow precise positioning of a spring-loaded plunger directly on top of the problematic component.
Many variations of this design are available to meet the specific needs of each individual PCB.
While a standard "flat foot" spring loaded plunger will handle most "floating" or "lifting" situations, other options available for use with this design include: Variable spring pressures; custom feet designed to hold down even the oddest shaped component; longer or shorter pin plungers for taller/shorter components; and, multiple grooves for holding a large number of pin plunger housings.
This versatility allows for many different component sizes, shapes and locations to be simultaneously held down during the wave solder process.
In addition, the Universal Top Hat can be used to hold the center of larger PCB's down against the pallet, or (through the use of a cone shaped foot) to seal off large through-holes from the wave.
While the need to hold down components is unique to the many and varied PCB's, DMI International's Universal Top Hat is able to provide many options that were previously only available in a custom designed and dedicated wave solder pallet.
DMI's Universal Top Hat can be built to fit and mount on any fixture with bars.
Further, the entire assembly can be moved from one fixture to another.
The universal top hat can be fitted with interchangeable tips for any application.
Lastly, this specialized and uniquely adaptive apparatus can be used for testing and verification of floating components, or as a permanent remedy for eliminating defects.
DMI International
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