EMI Shielding Cases CNC Machining for Sensitive Electronics

Aluminum 6061-T6 has 40 percent IACS (International Annealed Copper Standard) rated electrical conductivity, reflecting and attenuating 60–100 dB shielding effectiveness across 100 kHz to 10 GHz frequency ranges, and reflecting., Low density 2.70 grams per cubic centimeter reduces 60 to 70 percent enclosure weight versus steel equivalents for portable and aerospace applications. 276 MPa yield strength supports the structural rigidity of internal components weight 0.5 to 10 kg, a nd limits deflection to below 0.5 mm, and superior machinability allows complex geometries to be made, such as RF connector cutouts, honeycomb vent patterns, and removable gaskets with grooves, and tolerances ±0.003 inches. Copper C11000 has 101 percent IIACS-rated electrical conductivity with exceptional shielding effectiveness of 80 to 120 dB, especially at higher frequencies 1 to 40 GHz. 391 W/m·K thermal conductivity copper promotes heat dissipation from internally located electronics and aids in semi-conductor junction temperatures to be maintained below 85°C, and 10+ years of shielding performance in humidity 40 to 95 percent with corrosion resistance attributed to natural patina with internal shielding and primary external patina, and electroplating process compatibility of nickel or tin coatings 2 to 10 microns which prevent oxidation and lowered contact resistance of removable gaskets to below 2.5 milliohms during current flow.
After annealing, Mu-metal (an 80Ni-5Mo-Fe alloy) has a magnetic permeability of 20,000 to 100,000, meaning that the alloy provides low-frequency magnetic field shielding with an attenuation of 40 to 60 dB at 50 to 400 Hz power line frequencies. This outperforms aluminum and copper, whose effectiveness drops below 20 dB. Mu-metal also provides shielding of near-field magnetic sources with 20 to 40 dB in welded or mechanically-joined aluminum assemblies because of the deep-drawn seamless enclosures that eliminate aperture leakage paths, thus controlling reflection loss.

5-axis CNC machining centers with spindle speeds of 15,000 to 40,000 RPM manufacture complex cases with dimensional accuracy varying ±0.003 inches for enclosures of 50 to 500 millimeters for RF connector cutouts, honeycomb ventilation arrays, and internal mounting bosses. Using carbide tools of 1 to 20 millimeters in diameter and 2000 to 8000 millimeters per minute feed rates, intricate cases are executed. Dimensionally precise surface grinding operations of 0.002 inches per 100 millimeters flatness and Ra 0.4 to 1.6 microns surface finish. This ensures uniform conductive gasket compression of 15 to 40 percent, and contact resistance of less than 2.5 milliohms per linear inch is used for sealing the gaskets, providing uniform compression. Wire EDM cutting honeycomb vents are engineered for patterned honeycomb vents with cell 2 to 10 millimeters, wall 0.3 to 1.0millimetersr, and waveguide-below-cutoff characteristics allowing airflow and attenuating 60 to 100 dB of EMI above cutoffs of 18 to 90 GHz. CNC milling machine plans with gasket groove profiles where the width to ±0.005 inch and the depth of 0.5 to 2.5 millimeters.
We are cutting cases using a fiber laser, 500 to 2000 watts, cutting sheets 0.5 to 3.0 mm thin wall cases. We are eliminating edges with sealing gaskets while cutting using a laser. For copper and brass material, we perform CNC turning operations using multi-axis lathes. And for precision RF connectors, we made cylindrical shielding enclosures with a tolerance of ±0.002 inches on the diameter and a concentricity of 0.005 inches.

We achieve gasket sealing surface flatness of 0.002" over 100 to 400 mm perimeters. This ensures conductive gaskets compression 15 to 40% uniformly, clasping for shielding continuity with contact resistance lower than 2.5 milliohms per inch RF shielding. This prevents leakage through seams that would greatly degrade attenuation from the designed 80 dB down to 40 dB. The position accuracy of RF connector cutout is within ±0.003" which ensures coaxial alignment and prevents impedance discontinuities which would degrade VSWR from 1.2:1 to 2.0:1. There is a wall thickness precision of ±0.005" for a sheet of 0.5 to 6.0 mm which controls skin depth effect and maintains a shielding effectiveness of within ±5 dB of the theoretical value for the perpendicularity of the walls. We also maintain transverse perpendicularity of adjacent surfaces to 0.003" over 100 mm, which ensures the closure of the lid is parallel and prevents the compression of the internal gasket from varying more than 20%. Over the set design limits for performance, the position accuracy of the honeycombs vent cells maintains the cutoff frequency to within ±10% and the shielding performance above the set design limits. Each of the board mounting features is designed to maintain the position accuracy of holes to ±0.005," which ensures that the alignment of the PCB is within 0.15mm and that it engages the RF connector freely without stressing the circuit boards.

Of course, Zintilon offers rapid prototyping by delivering 5 to 20 functional prototypes within 2 to 4 weeks for testing shielding effectiveness in calibrated TEM cells and reverberation chambers, all validating attenuation performance per MIL-STD-461 and IEEE 299 standards. Zintilon also does low-volume production of 100 to 1,000 cases for specialized military and medical equipment while providing full dimensional reports and shielding test data. Zintilon continues with high-volume production of more than 10,000 cases per year for commercial electronics and telecommunication equipment. Zintilon provides automated inspection systems for each production phase. Zintilon employs a coordinate measuring machine with 0.003 millimeter repeatability for dimensional inspection, verifies surface flatness of gasket sealing surfaces to within 0.002 inches, and tests contact resistance at less than 2.5 milliohms at gasket interface using four-wire Kelvin measurement to validate electrical continuity. Attestation of shielding effectiveness is in anechoic chambers measuring attenuation 40 to 120 dB across frequencies 10 kHz to 40 GHz by IEEE 299 and MIL-STD-461 methods. Zintilon also conducts dimensional compliance checks to MIL-DTL and ISO 9001 with full traceability of materials to military standards.

All manufacturing processes are in accordance with ISO 9001:2015 quality management systems. There are documented procedures, material certifications, and process control systems for maintaining electromagnetic compatibility performance. Shielding cases comply with MIL-STD-461G electromagnetic shielding and also for the specific standards listed: RE102 for radiated emissions 2 MHz to 18 GHz, CE102 for 10 kHz to 10 MHz emitted, and RS103 for radiated susceptibility 2 MHz to 40 GHz with 20 to 200 volts per meter and 1 meter distance, FCC part 15 class A and B emitted limits for radiated and conducted emissions of commercial and consumer electronics, CISPR 11 and CISPR 22 for EMC on industrial and information technology equipment, and CISPR 25 for EMC in automobiles for the 150 kHz to 2.5 GHz portion. Testing to validate shielding effectiveness includes the IEEE 299 standard for measuring attenuation in shielded enclosures, MIL-STD-188-125 HEMP, and RTCA DO-160 for electromagnetic interference on avionics. These certifications include documentation for IACS values of 28 to 101, measured surface resistances below 2.5 milliohms per square for layered conductive coatings, and commercial compliance with RoHS, REACH, and conflict minerals.

The options for surface finishing for EMI shielding cases include conductive anodizing of aluminum, where an oxide layer of 5 to 25 microns is formed with a surface resistance of 5 to 50 ohms per square, maintaining shielding effectiveness within 5 dB of bare metal finishing, and protecting against corrosion. There is also the option of chromate conversion coatings per MIL-DTL-5541 which forms a conductive layer 0.3 to 1.0 microns thick with contact resistance of less than 2.5 milliohm for temporary corrosion protection and paint adhesion, and the option of corrosion resisting and solderable electroless nickel plating 5 to 15 microns thick on aluminum and copper for board-level shielding cans with reflow compatibility of 240 to 260°C and of course, tin plating (2 to 10 microns) on copper to prevent oxidation and assure contact resistance below 1.0 milliohm for gasket interfaces during the 8+ year service life. Finally, conductive paint coatings made of nickel or silver for plastic enclosures with electromagnetic shielding to achieve surface resistance of 0.01 to 1.0 ohms per square.
The particular treatments performed on the copper involved the use of special chemicals to create mirror-finished surfaces with finishes between Ra 0.1 to 0.3 microns. This focuses on improving RF performance in the millimeter-wave range of 30 to 100 GHz, where finely worked surfaces cause roughness loss increasing the surface roughness loss. Also, mu-metal was placed in an oven at 1100 to 1200°C in a hydrogen atmosphere to maximize permeability to between 80,000 to 100,000 for optimal low-frequency magnetic shielding below 1 kHz, and precision lapping for gasket sealing surfaces to a flatness of 0.001 inches and a finish Ra 0.2 to 0.4 microns to ensure BeCu fingers with closure forces of 50 to 200 grams per linear inch contact resistance uniformly below 1.0 milliohm per finger.

For straightforward two-piece aluminum shielding cases sized between 50 to 200 millimeters, with basic gasket grooves and connector cutouts, the entire process from material procurement, CNC machining, surface finishing, to testing the shielding effectiveness takes 3 to 5 weeks. For more intricate multi-chamber cases, which include machining multi-chamber cases with honeycomb vent panels, many RF feedthroughs, and precision gasket sealing surfaces, these take 6 to 9 weeks because the process involves wire EDM, precision grinding, and hermetic sealing validation. For rapid prototypes to support electronics development, functional shielding cases can be ready in 1 to 2 weeks with CNC machining from stock materials. For large production orders greater than 5,000 cases for commercial electronics, the initial setup up which includes machining fixture development, gasket tooling procurement, and first article shielding testing, takes 8 to 12 weeks, and the shielding must be tested in certified chambers against MIL-STD-461 or FCC requirements. After this, the shields will be delivered in batches of 500 to 2,000, which are synced with the PCB assembly schedule.

Certainly, we do custom-instrumented EMI shielding enclosing medical devices to RF removable shielding. Our space shielding incorporates an optimum design for size reduction to log periodic arrays with high compliance testing. Our testing setup enables achieving high compliance testing of field cavity shields by acoustically isolating them to ensure full attenuation of cavity reverberation to measure high levels of shielding. For military quantum computing systems, we implement nested multi-layer designs with ferromagnetic outer shells with high-conductivity inner linings spaced 10 to 50 millimeter air gaps, achieving over 140 dB shielding on multi-band RF. For generalized avionics, we use aluminum-lithium alloys to reduce weight by 10 to 15 percent while maintaining 60 to 80 dB shielding. Our vibration testing design enables testing to survive 5 to 2000 Hz at 20 g with full acceleration. Medical devices with glass-tometal hybrids meeting hermetic shielding while achieving IP67 environmental sealing for implantable devices or surgical instruments, and seamless hermetic glass with feedthroughs for bleeds, provide 76.2 dB shielding and electronics.

Minimizing surface contact resistance to below 2.5 mΩ/in and optimizing electromagnetic isolation in a 100-400 mm perimeter shield case are made possible through precision machining. This determines uniform conductive gasket compression of 20-35% which has an impact on contact leakage through gaps. RF leakage through gaps that weaken shielding effectiveness from a theoretical 100 dB to a 40-60 dB loss at frequencies of 100 MHz to 6 GHz can be eliminated through seam contact resistance control. RF connector cutout control to ±0.003 inches allows precision coax alignment for impedance discontinuities control. This drive VSWR from a designed level of 1.2:1 to 2.0:1 and insertion loss from 0.3 to 1.5 dB signal degradation for communication links operating in a range of -90 to -20 dBm. The composite material selected for the open gasket groove, whose dimensions were controlled to ±0.005 inches, widths of 3 to 8 mm, and depths of 0.8 to 2.0 mm, optimizes under-gasket compression to avoid contact resistance of over 10 mΩ. Over compression is to be avoided for a permanent set to occur, which is above 50% after 1000 open and closing cycles.
The dimensions of honeycomb vent cells, being accurate to +/- 0.008 inches, ensure that the vent cells' cutoff frequency remains within +/- 10 percent. This confirms that the vent cells will perform as designed when placed in a waveguide-below-cutoff shielding situation will provide shielding performance of 60 to 100 dB above the design cutoff of 18 to 90 GHz, while allowing cooling airflow of 20 to 100 CFM and a pressure drop of 10 to 50 Pascal. Uniformity of wall thickness within +/- 0.005 inches for sheets of 0.8 to 3.0 millimeters provides predictable skin depth effects, thus, maintaining the shielding effectiveness to within +/- 3 dB of the estimation based on material conductivity and frequency at the design life of 8 to 12 years in medical MRI systems operating at 0.5 to 7.0 Tesla field strengths, military communication radio systems that transmit 1 to 100 watts across 30 MHz to 3 GHz, and in aerospace avionics operating within the specified altitude and temperature ranges as well as precision instrumentation measuring the dynamic range specified.