Custom Interconnects, LLC
7790 E. Arapahoe Rd, Suite 250
Centennial, CO 80112
General Design Rules
1. Contact Pitch for each Fuzz Button diameter: .010" diameter = .4mm/.5mm,
.015" diameter = .65mm, .020" diameter = .8mm/1mm, .030" diameter = 1.27mm
2. Fuzz Button Compliance/Travel: 15 - 30% of length / 20% nominal
3. Minimum wall spacing between holes = .010"
4. Minimum spacing of hole wall to body edge = .010"
5, Recommended PCB pad plating: Hard gold over electroless nickel, 80 micro-inch gold over
200 micro-inch nickel over 0.5 to 1.0 ounce copper.
6. PCB pads should be larger than Fuzz Button diameter, round or rectangular in shape, with
maximum via size filled.
7. Lead traces are recommended to be buried with the PCB layers. If necessary, traces may
run on top side if covered by solder mask, which will eliminate shorting.
8. Solder mask must stay a minimum of .002" away from the perimeter of the PCB pads.
9. Recommended PCB minimum thickness is .062".
Interposers with Fuzz Buttons only
1. We recommend the Fuzz Button protrude on either side at .005" to .012" each in the
uncompressed state. This allows for easier alignment while also guarding against Fuzz
Button "fall-over" causing a short between two adjacent PCB pads. When the interposer is
sandwiched between 2 opposing PCBs, the Fuzz Buttons become flush to the surface plane.
2. Optimal travel for a Fuzz Button is 15 - 30% of its length in the uncompressed state, but
values outside of this range are usually acceptable, especially if only a single mating is
3. The holes in the interposer body should be just slightly larger than the Fuzz Button diameter.
Examples: For .020" Fuzz Button, holes should be .022" to .023", while for a
.010" Fuzz Button, the holes should be .011" to .012". This allows for easier insertion while also
ensuring the Fuzz Buttons remains in place during handling and assembly.
4. To aid insertion of the Fuzz Buttons, we recommend a 45 degree hole chamfer.
5. Minimum body thickness is .032" which supports the other stated design rules.
Test Sockets & Interposers with Fuzz Buttons & Hardhats
1. The body requires a 2 drill counterbore operation, whereby the bottom hole portion is larger
than the top portion. This ensures the Hardhat shoulder is stopped by the smaller hole
diameter, so the Hardhat does not come out of the top side.
2. The recommended Fuzz Button pre-load on the bottom side is .010", while the Hardhat on
the topside should be designed to protrude by .010" in the uncompressed state. Once
compressed, the Hardhat becomes flush to the surface plane.
3, The minimum recommended Fuzz Button length for this type of stack-up is .060", however, a
length of .080" to .100" would be more ideal to provide greater durability and travel.
Interposer/Socket Material Choices
Ultem® Ultem 1000 is our go-to material offering low out-gassing, superior
isolation, high structural strength and very light weight.
FR4 / G-10
Other dielectric plastics
Aluminum Alloys (many coatings/platings available)
Brass (commonly gold-plated)
RoHS Compliance Statement
Industry Publications and Resources
Microwaves & RF
Microwave Product Digest
High Frequency Electronics
Chip Scale Review
Semiconductor Packaging News
Global SMT & Packaging
Military & Aerospace Electronics
Aerospace & Defense Technology
JED - The Journal of Electronic Defense
Association of Old Crows