Fuzz Button Design Criteria There are numerous considerations when designing Fuzz Button test sockets and/or Fuzz Button connectors. These criteria are essential considerations for each individual application and should be factored into the ultimate design solution. Fuzz Button Compression Range Fuzz Buttons should be designed to be compressed 20% of their original height, nominally. The design should consider tolerance stack ups that provide for an absolute minimum compression of 15%, and an absolute maximum compression of 30%. For applications not meeting standard compression range requirements, contact the factory. Fuzz Button Length to Diameter Aspect Ratio Fuzz Buttons are available in length to diameter ratios of 2:1 minimum to 8:1 maximum. For longer or shorter Fuzz Buttons, contact the factory. Number of Insertions: The number of insertions required in the application is a critical consideration with regard to whether or not "Hardhat" contact pin(s) should be included into the design. Generally, connectors that require up to 20 insertions (mates/demates) can be designed with a stand alone Fuzz Button element. Designs requiring a higher number of insertions should include "Hardhat" contact pin(s) to protect the Fuzz Button from fraying, mushrooming and ultimately collapsing. Operating Temperature: The operating temperature is a critical factor with regard to specifying both the wire and plastic material types. Various materials are available to cover normal operating temperature requirements. Available Clamping Force: The amount of force available to compress the entire array of Fuzz Button is critical to obtain the proper deflection. On average, Fuzz Buttons require a minimum of about 45 grams each of force to reach the proper deflection range. Fuzz Button Handling and Retention: Standard Fuzz Button test sockets do not encompass features to retain the Fuzz Buttons and Hardhats, resulting in special handling requirments during mounting. Both fuzz buttons and hardhats are fully retained, once mounted to the PCB. Fuzz button connectors may or may not include special features for capturing and retaining the stand alone Fuzz Button elements. Current Carrying Capacity: In consideration of their small size, Fuzz Buttons can carry a significant amount of current. Typically, .020" diameter Fuzz Buttons can handle 4 amps continuous, with larger Fuzz Button diameters handling higher requirements.

Printed Circuit Board Design Criteria

There are a few special considerations for designing printed circuit boards (PCB's) to be used in conjunction with Fuzz Button test sockets and/or Fuzz Button connectors. These criteria should be followed to ensure proper alignment, mounting and electrical contact between the PCB and Fuzz Button connector or test socket. Alignment Pins: Typically Fuzz Button connectors and sockets require the incorporation of two alignment pins that plug into the PCB and align the contacts to the pads on the PCB. Unless there is some other consideration for alignment of the connector/socket to the PCB, alignment pins are are the prefered method. Standard alignment pins are .062", .093", or .125" diameter and should be designed to protrude out of the connector or socket to the thickness slightly below that of the PCB. The location of these holes in the board is critical, and requires a tight tolerance of +/- .001". Mounting Holes: Standard Tecknit sockets have brass inserts into which screws are inserted through the back of the PCB and into the socket. The screws are typically sized as 2-56, and require .094" + / -.002" holes drilled in the PCB at each mounting location. Connectors can also have inserts designed to accept screws, or can have through holes to sandwich the connector between PCB's. In This instance holes should be spaced at a maximum distance of 1.5" apart from one another, to minimize the chance of bowing of the connector itself or the PCB's. Top Layer PCB Traces: PCB traces may be run on the top side of the board if they are covered by solder mask to eliminate the potential for shorting. However, it is prefered that traces be buried within the layers of the PCB. PCB Vias: PCB vias are typically required to run buried traces to the surface PCB pads. Vias may be incorporated into the center of the PCB pad only if the via diameter is less than half of the Fuzz Button diameter. Otherwise, the vias should be "dog-boned" shaped and offset to the pad. Solder Mask: It is essential that any solder mask around the PCB pads be a minimum of .002" away from the perimeter of the pads, to avoid having the Fuzz Button sit partially on the solder mask. This condition would cause miss-contact (open) between the Fuzz Buttons and PCB. PCB Pad Plating: Typically, Fuzz Buttons utilize gold plated wires. Therefore, we recommend using gold plated pads, although it is not an absolute necessity. In most applications, Fuzz Buttons sit directly on the PCB pads and will not damage or wear the normal pad finish. PCB Minimum Pad Sizes and Shape: The following table indicates the minimum pad sizes for normal device pitches. Pad shape is left up to the individual designer, although we would prefer to match the round shape of the Fuzz Button to a round shape pad.

Recommended Pad Widths For Fuzz Buttons

Pitch	Current Fuzz Button Diameter	Recommended Pad Width	Maximum Via Size
2.54mm (.100")	.040"	.045" to .050"	.020"
1.27mm (.050")	.030"	.032" to .035"	.015"
1.0mm (.0394")	.020"	.023" to .025"	.010"
.8mm (.0315")	.015"	.020" to .022"	Fill Via
.75mm (.0295")	.015"	.018" to .020"	Fill Via
.65mm (.0256")	.015"	.016" to .018"	Fill Via

For reference only: To be used as a design guide only. Recommend gold plated PCB pads. Recommend round or rectangular pad shape. For other shapes contact the factory.

Standard Test Socket Hole Design Schedule

I. Hole A (Qty. 2) 1.) Purpose: A .093 dia. stainless steel locating pin is press fit in this hole. The pin extends a maximum of .125 inches below the bottom of the test socket surface, and is used to locate the test socket on to the board. 2.) Test socket hole dimensions: .093" dia. + .000/-.001. 3.) Circuit board dimension: Tecknit suggests that a .094" + .001/-.000 dia. hole be drilled through the circuit board. The location of these holes in the board is critical. II. Hole B (Qty. 4) 1.) Purpose: These holes are used for the installation of a top mounted style hand test clamp. The hand test clamp fits on top of the socket and is used when the area around the test socket is limited and the standard clamshell type clamp that extends past the outside of the socket cannot be used. 2.) Test Socket Dimensions: .110" dia. + .005" / - .0015" through hole. Counter bored far side .144" dia. + .005" / - .001" x .040" deep. 3.) Circuit Board Dimension: None required. III. Hole C (Qty. 8/10 depending on available board space) 1.) Purpose: These holes are drilled in the test socket so that a 2-56 brass insert can be installed from the topside of the test socket. This insert is used to secure the test socket to the circuit board, by using eight/ten screws that pass into holes drilled through the circuit board. ( 10 holes are preferred; 3 each side, 2 top and 2 bottom, to assure flatness of the test socket with respect to the circuit board.) 2.) Test Socket Dimesion: .110" dia. + .005" / -.0015" through hole. Counter bored near side .144" dia. + .005" / -.001" x .040" deep. 3.) Circuit Board Dimension: Tecknit suggested that an .094" dia. + .002" / -.000" through hole be drilled as a clearance hole in the board to accept the 2-56 screw that is used to secure the test socket to the circuit board. ( Head style of screw is at discretion of customer.) IV. Hole D and D1 (1 ea.) 1.) Purpose: To accept press fit Torlon bushings, Tecknit P/N 92-30000 at D (round hole) and Tecknit P/N 92-30001 at D1 ( oval hole ). These bushings act as guides for the alignment pins on the Delta-Flex handler chuck. 2.) Test Socket Dimension: .300" dia. + .000" / -.001" through hole. 3.) Circuit Board Dimension: No holes are required in the board, but the alignment pins on the handler must fit the .186" +/- .001" inside dia. hole of the bushings. Hole Design Positions