Polymer coatings and metallic electroplating can be applied to many medical grades, such as F562, 304VM, 316LVM, and other alloys depending on the medical application. Coating the wire prior to incorporating it into a device provides more complete coverage over the entire surface area of the wire, rather than strictly on the outside of a device.
The polymer coatings can provide a dielectric barrier when the wire in the device is used to transmit electrical signals or provide electrical current for medical therapies. Polymer coatings can also be used for ionic barriers, enhanced corrosion resistance, providing a lubricious surface and/or be used for lead identification.
Electroplated coatings can be used to enhance the joinability of the base wire grades (i.e. solderability, weldability, ultrasonic bonding etc), increase the conductivity and/or provide a more noble surface.
PTFE is used as a coating on fine wire for either dielectric protection or to enhance lubricity. Aqueous based PTFE is typically applied to precious metal alloys such as PtIr of less than 0.100 mm and is clear in color. Solvent based PTFE is applied to the wires in the 0.1 mm to 0.8 mm range for applications such as catheter guide wires. The solvent based PTFE grades provide a balance between good adhesion and good lubricity in these applications. They are supplied in various colors such as green, blue, grey and clear.
Electroplating and polymer coating can be performed on square and ribbon wires in addition to round wires.
Sandvik's speciality is gold plated copper (0.02 mm and larger) but plating on a wide variety of other metals is possible (i.e. nickel, nickel chrome, silver and copper alloys). Nickel plating and/or a nickel interlayer is also possible.
Polymer coated wires can be combined in multifilar configurations such as bifilar, trifilar, quadfilar etc. Multifilar wires simplify wire handling when multiple signals are required for a device. Multifilar wire cables can be provided in a flat or bundled configuration and eight different colors and multiple shades of these colors are available for easy identification. Common uses of multifilar coated wires are bifilar pairs for medical microthermocouple applications and quadrfilar goldplated copper leads for sensor signal transmission.
The primary use for polymer coated, precision medical wire is in sensor applications in vivo diagnostic and in therapeutic procedures, where electrical signals or currents are conducted micro-invasively. Key product features of the Sandvik medical wirrange include small diameter (approx. 0.025 mm) variety of polymer coatings, offered either as standard or as custom-coated to precise requirements and specifications. The extremely thin coatings, applied in a uniform and pinhole-free way, guarantee excellent electric isolation properties. Typical end use applications include heart mapping devices, blood pressure and temperature measuring equipment, tissue temperature sensors and brain sensors.
Common uses of multifilar coated wires are bifilar pairs for medical micro-thermocouple applications and quadfilar goldplated copper leads for sensor signal transmission.
While many of these applications did not exist five to ten years ago, developments in coating technology, coupled with the cooperation between device manufacturers and material suppliers, has resulted in improved product performance, reduced trauma and new product features, allowing medical procedures that were not previously possible.
The coating method used is called "flood coating". This method allows for tight dimensional controls and ultrathin wall thicknesses. An older process for Teflon coating, still in major use today, is "electrostatic spray coating" which is applied to a finished medical device. The flood process offers some advantages over the electrostatic process, including improved adhesion of PTFE to the wire, cosmetic enhancements and thickness control.
The standard dielectric polymer coatings can be manufactured in accordance with the National Electrical Manufacturers Association (NEMA) standards listed below or be modified to meet customer specific requirements (ie ultrathin build not listed in NEMA)
|Solvent based||Water based|
|Coating||Polyamid ; Polyester; Polyesterimide;
Polyethersulfone; Polyphenylsulfone; Polyimide ; FEP; Polyurethane; Polyvinylacetyl
|Single pass flood coating process
thickness max : 0.00635mm (0.00025 in.)
Coating : Au, Ag, Cu, Ni
The electroplating method is reel to reel in order to provide continuous lengths of coated wire. The plated surface can be provided in an as plated condition or can be further processed (drawn, annealed) to the finish size after plating. Other electrochemical techniques (anodizing, electropolishing, electrocleaning) are also available to provide surface modifications to metal wire surfaces. Anodizing is used to chemically oxidize aluminum alloys for improved dielectric strength.
Note : Electrical testing that can be performed on these materials includes: dielectric breakdown tests in air or saline solution, continuity tests and pin hole testing.
Exera® Insulating coating
|NEMA MW 1000 spec.||General comments|
|Formvar||Polyvinyl Acetal insulation||105||MW15-A,C||Excellent flexibility, abrasion resistance and chemical stability|
|4025 Polyurethane||Polyurethane insulation||130||MW75-C||Long term cure stability. Easily solderable|
|Excellent dielectric properties and easily solderable|
|Poly/Nylon||Polyurethane with polyamide topcoat||155||MW28-C
|Easily solderable; abrasion resistant & easier winding|
|Poly180B||Polyurethane insulation||180||MW79-C||Highest temperature Polyurethane - easily solderable|
|TRI-2-SOD||Solderable polyester-imide insulation||180||MW26-C
|High temperature capability solderable insulation|
|TRI-2-SOD/Nylon||Solderable polyester-imide with polyamide topcoat||155||MW27-C||Solderable Polyester with the toughness/windability of Nylon|
|Polyclad||THEIC modified polyester insulation||200 for copper
220 for aluminum
|Temperature stability of Polyester|
|Polyclad/Nylon||THEIC modified polyester
with polyamide topcoat
|180||MW76||Temperature stability of Polyester with the toughness/windability of Nylon|
|Polyclad/Aminid||THEIC modified polyester
with polyamide-imide topcoat
|200 for copper
220 for aluminum
|Increased temperature capability over POLYCLAD N.|
|Estmide||Polyester-imide insulation||180||MW30||Good temperature stability, solvent resistance and windability|
(also usable as topcoat)
|220||MW81-C||High temperature insulation with lubricity & chemical resistance|
|PAC 240||Aromatic polyimide insulation||240||MW16;
|Highest temperature capability with good chemical resistance. Mechanically strip before soldering|
|Teflon R||Polytetrafluoroethylene insulation||260||None||Excellent thermal, dielectric and chemical resistance|
Typical specifications for gold plated copper wire
Standard thickness Polyurethane insulation
|44 AWG||46 AWG||47 AWG||48 AWG||50 AWG||51 AWG||52 AWG|
|Bare wire diameter (in.)||0.00190
|Gold plating thickness (microinches)||70 +/- 20||70 +/- 20||70 +/- 20||70 +/- 20||45 +/- 20||45 +/- 20||45 +/- 20|
|Insulation wall thickness (in.)||0.000210
|0.000190 +/-0.00006||0.000175 +/-0.000065||0.000155 +/-0.00006||0.000120 +/-0.00005||0.000110 +/-0.00005||0.000100 +/-0.00005|
|Min. break load (grams)||44||30||25||20||12||9||7|
|Min. percent elongation||16%||14%||13%||12%||7%||7%||7%|
|Resistance min/max (ohms/meter)||8.8/10.8||12.9/16.3||16.4/20.5||22.6/26.1||33.0/41.0||41.8/53.4||52.9/67.9|
|Min. dielectric strength (Volts/mil)||1500||1500||1500||1500||1500||1200||1200|
|Reference weight (grams/cm)||0.1855||0.1307||0.1060||0.0849||0.0521||0.0420||0.0338|