Pressure Application

Proper pressure application ensures reliable contact between test probes and the Device Under Test (DUT). Two primary methods deliver controlled downward force: pressure pins for standard applications and pressure pads for specialized needs.

Pressure Pins#

Pressure pins deliver controlled downward force on the DUT, ensuring reliable contact with the test probes below. They mount to the pressure plate and engage specific points on the board surface.

Materials#

Pressure pins are manufactured from engineering plastics:

• Acetal (Delrin) — Standard choice for most applications
• POM (Polyoxymethylene) — Alternative with similar properties

These materials provide durability while avoiding damage to board surfaces and components.

Standard Lengths#

Ingun Fixture Details#

For Ingun fixtures, pressure plates feature a 7mm diameter countersink that's 3.2mm deep. This accommodates standard 6mm diameter pins while optimizing force distribution for 1.6mm thick PCBs.

Placement Guidelines#

• Position pins over rigid areas of the PCB (away from flex regions)
• Align with component-free zones to avoid crushing parts
• Distribute pins to provide even pressure across the board
• Consider probe locations—pins should push the board toward probe contact points

Pressure Application Pads#

For specialized applications, a pad system combines a rigid plate with a compliant layer:

• Rigid plate — Polycarbonate or acrylic backing
• Compliant pad — Polyethylene foam layer

When to Use Pads#

Pressure pads suit applications where pins are impractical:

• Flex and rigid-flex PCBAs — Distributed pressure prevents board damage
• High-density boards — No component-free zones for pin placement
• Sensitive components — Pad distributes force to avoid point loading

Mounting#

The pad assembly secures to the pressure plate using M3 or M4 standoffs. This maintains consistent pressure distribution across the DUT surface.

Selection Guide#

Best Practices#

1. Match pin length to fixture — Use specified lengths for your fixture type
2. Secure pins properly — M3 x 10mm screws prevent pins from backing out
3. Check pin condition — Replace worn or damaged pins
4. Verify contact — Confirm probes make contact with pins engaged
5. Balance pressure — Distribute pins/pads for even force application

Related Documentation#

• Fixture Bases — Pin length specifications by fixture
• Dev Fixture Guidelines — Dev series pressure setup
• Ingun Guidelines — Production fixture pressure