Laird Technologies has introduced its Sentry Form-in-Place conductive gasket materials. The new product line is replacing existing form-in-place conductive gasket materials. The new Sentry materials provide enhanced mechanical properties, increased adhesion to substrates and higher EMI shielding performance.
Sentry conductive gasket materials are one-part materals and include moisture cure (22 C and 50% relative humidity for 24 hours) and thermal cure (125 C for minimum 1 hour). Sentry conductive gasket materials are comprised of silicone with conductive metal filler, either silver plated aluminum, silver plated copper, silver plated nickel or low cost silver plated graphite. Generally, it is recommended to use filler with same material as substrate to minimize galvanic corrosion potential, i.e., use silver plated aluminum if applying the gasket onto an aluminum substrate.
The table below summarizes properties of new Sentry conductive gasket materials.
|
Property |
Units |
SNL60-RXP |
SNK55-RXP |
SNN60-RXP |
|
Elastomer |
|
Silicone |
Silicone |
Silicone |
|
Filler |
|
Silver Plated Aluminum |
Silver Plated Copper |
Silver Plated Nickel |
|
Volume Resistivity |
ohm-cm |
0.003 |
0.002 |
0.005 |
|
Shielding Effectiveness |
dB |
>100 |
>90 |
>100 |
|
Hardness |
Shore A |
60 |
55 |
60 |
|
Tensile Strength |
kPa |
850 |
1300 |
192 |
|
Tensile Elongation |
% |
140 |
300 |
110 |
|
Compression Set |
% |
10 |
10 |
15 |
|
Adhesion to Al |
N/cm2 |
140 |
200 |
180 |
|
Compression Deflection |
|
|
|
|
|
at 20% Compression |
lb/in |
1.9 |
1.2 |
1.7 |
|
at 40% Copression |
lb/in |
8.3 |
5.2 |
6.4 |
|
Temperature Range |
°C |
-50 to +125 |
-50 to +100 |
-50 to +125 |
|
Flamability Rating |
UL94 |
V0 |
V0 |
V0 |
EMI shield effectiveness over a broad frequency range provide designers with tools to control EMI emissions as well as mitigate cross talk between compartments of electronic devices. The table below provides EMI shielding for SNN60-RXP (silver plated nickel filled silicone) over frequencies from 100 MHz to 20 GHz.
Cybershield has available inventory of many of the Sentry Conductive gasket materials for customer sampling and evaluation.
Form-In-Place gasket is a conductive elastomer comprised of silicone with filler of silver plated copper, nickel, aluminum or graphite particles to provide EMI shielding, grounding and environmental seal gaskets onto metal or plastic substrates. The EMI gaskets can be dispensed onto any conductive painted, plated, or metallic surface. The conductive gasket typically makes electrical contact between the conductive surface of the enclosure and the ground-plane on the PCB, thereby containing the EMI within the shielded area, or at the interface between the mating surfaces of enclosures to shield internal emissions and external interference.
The Form-In-Place conductive gasket is custom designed to meet the requirements for the space, path and compression force. The gasket is dispensed using computer controlled robot that precisely locates the gasket onto specified locations of the part. The gasket can be one continuous path around the perimeter of the part to provide EMI shielding and/or environmental seal. The conductive gasket can also be dispensed in intricate paths around numerous compartments to prevent cross talk between electronic components within the system. The gasket path can be easily changed by re-programming the robot in order to accommodate changes in requirements or design. The process is suitable for lot sizes of 1 unit to millions of units per year. Gaskets are single component material, dispensed at room temperature.
Form-In-Place Technical Specifications:
- Operating temperature range of -58 to 257°F (-50 to 125°C)
- Low compression force, typical 1.5 Lbs/linear in. (0.27 Kg/cm)
- Size range: Height: 0.015” to 0.090” (0.38 mm to 2.3 mm), Width: 0.018” to 0.125” (0.46 mm to 3.1 mm)
- UL-94 V-0 flammability
- Working compression range from 10% to 50% of the gasket height, with a recommended design compression of 30% against a mechanical compression stop
- Typical volume resistivity of 0.002” ohms-cm
- EMI shielding effectiveness >100 dB from 100 MHz to 10 GHz
Successful Form-In-Place conductive gasket applications include wide range of electronic equipment, including mobile devices, medical electronic equipment, military equipment, avionics, telecommunications base stations, industrial equipment, just to name a few.
Contact Cybershield for more information or technical data
Conductive paints are comprised of micron sized metal particles of nickel, copper, silver plated copper or silver blended into water or solvent based paint system. Similar to selective plating process, a masking fixture is used to control the location of the conductive paint that is sprayed onto the required areas of the part. The fully cured conductive paint thickness ranges from 0.0005” (0.0125 mm) to 0.002” (0.05 mm) depending on the paint type and EMI shielding requirement. The paint can be applied in a manual paint booth where an operator applies the paint with a paint gun or with a paint robot. The paint robot offers advantages over manual spray methods, especially in higher volume applications where cost is critical. In the robot, the spray pattern can be programmed and frozen to apply the optimal amount of conductive paint across the entire shielded surface. Manual paint application typically has lower set-up cost than robotic painting and is a good match with lower volume applications.
Table summarizes compatible resins with conductive paint. Difficult to paint resins will usually require primer or other surface preparation prior to the conductive paint process.
|
Common Paintable Resins
|
|
ABS
|
Polycarbonate (PC)
|
Polybutylene Terephthalate (PBT)
|
|
PC/ABS
|
Poly Aryl Amide
|
Polyphenylene Oxide (PPO)
|
|
PC/PBT
|
Polyphthalamide (PPA)
|
Polyether Imide (PEI)
|
|
Nylon
|
Polystyrene (PS)
|
Polyphthalamide (PPA)
|
|
Difficult to Paint Resins (May Require Primer)
|
|
Teflon (PTFE)
|
Polyethylene
|
Liquid Crystal Polymer
|
|
PEEK
|
Polyimide
|
Polypropylene
|
Painting Design Issues
|
Design Don’t
|
Design Alternative
|
|
Difficult to Paint Tight Bosses, Crevices and Holes
Line-of-Sight Paint Process
|
Eliminate Crevices & Small Holes Requiring Coating
|
Secondary Operations:
Inserts can be molded into the part or installed by heat staking or ultrasonic insertion prior to or after paint application.
Gaskets for environmental or EMI/RFI seal are installed after painting. Form-in-place gaskets, comprised of silicone with metal particle filler can be dispensed around perimeter of compartments of plastic part (or metal part) to prevent interference within the device and/or around the perimeter of the enclosure to provide an EMI seal from the external environment.
Specifying the conductive paint system includes the following elements:
- Dry Film Thickness is usually defined as a minimum. If required, due to part function or fit, plating can be specified as a thickness range.
- The coating resistance can be specified, either in ohms per square or point-to-point ohms resistance. In this case, paint thickness need not be specified.
- Coating adhesion is commonly measured according to ASTM D3359 Standard. This standard is based on tape test and 1-5 scale for amount of coating removed during the tape test (5 is no metal removed and 1 is complete removal of the coating).
This newsletter includes overview of several EMI shielding applications.
Shielded Connectors
Connector designs in today’s electronic equipment face the competing demand for a smaller form factor, lighter weight, improved mechanical performance, increasing need for EMI shielding, and lower cost. Metal shells, used to shield connectors, add weight, cost and space. Plated plastic connectors are being used to meet the EMI/RFI shielding requirements, reduce weight and space. Nickel thickness can be varied between 50 and 600 micro-inches (1.25-15.0 µm) to meet mechanical and environmental requirements.
Medical Electronic Device
Shielding medical electronic devices is significant design issue due to the pervasiveness of electronic equipment in the hospital. Autocatalytic selective plating and conductive paint are applied onto many medical electronic device enclosures to provide EMI shielding.
Military Electronic Equipment
The modern day battlefield is noisy, and military electronic systems need to be shielded against EMI/RFI noise. With move to rapid force deployment, this drives the need for lightweight mobile electronic systems. Plastics have made significant inroads into the electronic battlefield. Since plastics do not shield against EMI/RFI, they are usually shielded, often with thick electroplated coatings to protect against wide EMI/RFI frequency range that may be encountered in the field. The plated plastic components can then be coated with mil-spec finishes, including latest generation water borne Chemical Agent Resistant Coating (CARC) paint.
As with resin selection, plastic part design is critical to successful application. There are design approaches that should be avoided if possible.
|
Design Don’t
|
Design Alternative
|
|
5-sided Box or Cup Design Trap Air and/or Drag Out Plating Chemicals
Impact Plating Quality & Cost
|
Include Drain Holes
Design Part to Prevent Entrapment of Air or Plating Solution
|
|
Tight Crevices Can Trap Plating Solution
|
Eliminate Crevices in Design or Include Drain Hole
|
|
Small Blind Holes
Trap Plating Solution
Later Weep Out & Damage Plating
|
Utilize Through-holes
If Blind Holes Required, Plug to Prevent Plating Solution Entrapment
|
Another issue includes inserts, which can be molded into the part or installed by heat staking or ultrasonic insertion prior to or after plating. If specifying <100 micro-inches (2.5 µm) electroless plating thickness, inserts can be installed before or after plating. If plating thickness >100 micro-inches (2.5 µm), inserts should be installed prior to plating and masked during the plating operation with a plug or screw to prevent plating on the threads. Standard boss and insert design guidelines should be followed for plated plastic parts with inserts, and brass inserts are compatible with electroless and electroplating plating processes. Photo below shows automated insert installation using heat staking. Ultrasonic insertion is also available.
Conventional finishing operations such gasket installation for environmental or EMI/RFI seal, decorative paint, and part labeling can be used to finish the plated plastic part to final OEM specifications. Material selection for gaskets, decorative paint and label ink are determined by the final plating metal layer on the part. Photo below shows plated plastic faceplate with fabric over foam conductive gaskets, and latches installed and decorative paint.
Specifying the plating system includes the following elements: - Thickness is usually defined as a minimum. If required due to part function or fit, plating can be specified as a thickness range. Plating thickness is commonly measured using X-ray fluorescence, a non-destructive test with accuracy down to 2x 10-7 inches (0.005 µm). Note modern X-ray equipment can measure up to 3 unique metal layers o a plated plastic part.
- Where surface conductivity is critical due to application as EMI/RFI shield or ESD coating, the coating resistance should be specified, either in ohms per square or point-to-point ohms resistance. In this case, plating thickness does not need to be specified.
- Plating adhesion is commonly measured according to ASTM D3359 Standard. This standard is based on tape test (either destructive or non-destructive) and 1-5 scale for amount of plating removed during the tape test (5 is no metal removed and 1 is complete removal of the plating).
Plating on plastic technology was first developed in the mid 1980's to improve EMI shielding of electronic devices. A number of "plateable" resins such as ABS and Polycarbonate/ABS blends were developed at that time by resin manufacturers to enable plating on plastic. Since then, there has been significant advancements in the technology. Today, a wide range of plastic resins can be plated. See the table below for listing of resins that can be plated. The top section is comprised of resins that are widely plateable. The middle section of the table includes resins that have mixed plating results - some grades within these families are plateable while some are not. Also, there are some resins, such as Polypropylene (PP), which are normally not plateable; however, if the PP is compounded with a plating additive, it can be successfully plated. Finally, the bottom section of the table is comprised of resins that are very difficult or even impossible to plate.
Plateable Plastic Resins
Widely Plateable
- ABS
- Polycarbonate (PC)
- Epoxy-Graphite
- Liquid Crystal Polymer (LCP)
- PC/ABS
- Polyetherimide (PEI/Ultem) >20% Glass Fill
- Polystyrene
Photo below shows range of plated connectors molded in PC/ABS as well as PEI.
Selected or Custom Blended Plateable Grades
Note that only selected grades within these resin families are plateable. Alternatively, the plateable grades within these families may require custom blending to include plating additive in order to be plateable or they require non-conventional plating process (such as grit blasting prior to plating) to be able to plate.
- Polyphenylene Oxide (PPO/Noryl)
- Liquid Crystal Polymer (LCP)
- Fiberglass
- Graphite
- Epoxy
- Polyetheretherketone (PEEK)
- Polyphenylene Sulfide (PPS)
- Urethane
- Polyphthalamide (PPA/Nylon)
Not Plateable
- Polybutylene Terephtalate (PBT)
- Polyethylene (PE)
- Polyvinylchloride (PVC)
It is essential that resin that is compatible with plating technology be selected. This can lead to successful application.
 |
| Plated Mobile Antenna |
|
A good rule of thumb is that a plastic resin plateability is inversely related to the chemical resistance. The higher the chemical resistance, the more difficult to plate the resin. This is important because if you select a resin that is difficult to plate, you may see marginal or weak plating adhesion, which can lead to failures in the field when the plated plastic system is subjected to stresses from temperature changes and/or shock & vibration. If the plating has excellent adhesion when first deposited, it is likely to adhere to the plastic substrate for the life of the application even if subjected to harsh operating conditions.
Conclusion: resin selection should be determined early in the design cycle, and designers should seek to select a resin with good plating track record. The list of plateable resins is ever changing. When new resins are developed or grades within the resin families are added, Cybershield assesses the plateability of these resins. We are continually adding to our list of plateable resins. If you have a resin that you want to use and it is not on the list or you are unsure if it is a plateable grade, contact us.
The first step to a successful plating on plastic application is resin selection. The resin in the antenna waveguide application is PC/ABS, a low cost, plateable material. This application has been in production for several years in harsh outdoor use with excellent performance and reliability.