Overview

A custom invar probe spring is a micro-elastic contact — a cantilever, a tip and a locating frame — etched from Invar sheet for wafer test and probe-card use. A dry-film resist is imaged with the probe geometry, developed, and the exposed metal is dissolved, leaving burr-free edges with no stamping stress. Invar is an iron-nickel alloy with about 36% nickel whose dimensions barely change across a wide temperature range, with stock typically 0.05–0.5 mm. Because whole-sheet chemical removal does not alter the microstructure, a custom invar probe spring keeps its spring force and tip position consistent from sample to volume.

For test engineers, the custom invar probe spring addresses the most sensitive issues of wafer-level contact: thermal expansion shifts ordinary probe tips during hot and cold testing, a 0.1 mm arm snaps in a die, and a burr scratches the pad or destabilizes contact resistance. Etching forms the cantilever, tip and frame together, so changing arm length or pitch is a new film rather than a precision die, which suits multi-specification prototypes. Probe-card flexures, test-socket contacts, fine-pitch interposers and thermal-cycling fixtures all rely on low-expansion, fine, coplanar etched Invar probes.

Parameter Window

• Available Materials: Invar 36 (4J36, Fe-Ni36), Super Invar, Kovar, with 301 stainless as an alternative
• Material Thickness Range: 0.05–0.5 mm (0.1 mm and 0.2 mm for most cantilevers)
• Tolerance: ±0.015 mm on arm width, ±0.02 mm on tip position, ±0.05 mm on outline
• Minimum Feature: 0.1 mm arm width, 0.08 mm tip width, 0.2 mm probe pitch
• Surface Options: bare passivated, Ni/Au plating, stress-relief anneal, low-temperature set
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Artwork Review — Vectorize the probe array, check arm width, tip and pitch against stock thickness, and set the coplanarity datum.
2. Material Selection — Confirm Invar grade and expansion coefficient, check flatness, and align rolling direction along the cantilevers.
3. Cleaning & Lamination — Degrease and laminate dry film on both faces so no bubble or residue sits under fine arms and tips.
4. UV Exposure — Expose through high-resolution film registered to the sheet edge so every tip on the card lands consistently.
5. Development — Open the etch areas and inspect each fine arm under a microscope for complete development.
6. Etching — Spray Invar-matched chemistry with controlled time and temperature to stop fine arms thinning or breaking.
7. Stripping & Setting — Remove resist, neutralize, then stress-relief anneal and low-temperature set; Ni/Au plate to lower contact resistance.
8. Inspection & Packaging — Measure arm width, tip coplanarity and spring force against the sample, then pack in trays to protect fine tips.

Core Advantages

1. Near-zero expansion: Invar barely changes size across temperature, so tips do not drift during hot and cold testing and alignment holds.
2. Burr-free, low damage: Chemical removal leaves no stamping burr, so smooth tips do not scratch pads or plating.
3. Extremely fine arms: 0.1 mm arms and 0.08 mm tips form reliably, enabling fine-pitch probe arrays.
4. Whole-card coplanarity: Simultaneous etching makes hundreds of tips naturally coplanar, with no per-pin leveling at assembly.
5. Uniform spring force: No mechanical stress is added, so force and deflection match across a batch and contact resistance stays stable.
6. Thermal-cycle reliability: A custom invar probe spring combines low expansion with fine, burr-free etched geometry for full-temperature wafer test.

Typical Applications

• Probe-card flexures: Cantilever contact pins in wafer probe cards, where low expansion keeps tip position accurate over temperature.
• Test-socket contacts: Micro-elastic contacts in chip test sockets, gold-plated for low and stable contact resistance.
• Fine-pitch interposers: Elastic transition parts in fine-pitch board-to-board links with thin arms and repeatable spring-back.
• Thermal-cycling fixtures: Elastic press plates holding samples in hot and cold tests without dimensional drift.
• MEMS probe tips: Micro-probe arrays for MEMS devices that demand very high tip coplanarity.
• Precision locating springs: Low-expansion locating flexures in optical and metrology gear that add no displacement error with temperature.

Design Notes & Process Considerations

1. Expansion coefficient: Select the Invar grade for the test temperature range and state the allowed thermal drift; do not substitute plain stainless.
2. Arm-to-thickness ratio: Keep the finest arm at or above stock thickness; a 0.1 mm arm on 0.1 mm sheet needs an etch-factor allowance.
3. Grain and force: Orient cantilevers along the rolling direction, since cross-grain bending widens force scatter and lowers fatigue life.
4. Tip coplanarity: Call out whole-card tip coplanarity and its measurement datum, and unify the inspection method with an approved sample.
5. Plating and contact: Specify Ni/Au thickness and a contact-resistance ceiling, because a heavy plating changes fine-arm stiffness.
6. Sampling and lock: Approve a sample for arm width, coplanarity and force, then lock etch and set parameters for a custom invar probe spring before volume.