Medical Precision Winding, Medical Coil Engineering Assistance

• Self supporting coils
  • How bondable wire works
• Bobbin coil- micro molding
• Round VS rectangular ID
• Coils with special angles
• 150-180 C vs. 200-220 C magnet wire
• Stripping fine wire·
• What affects inductance

Bobbin coil- micro molding

• Using a bobbin will save 15-30% of the total coil cost.
  • Bondable magnet wire may not be required.
  • Bobbins provide possibilities for automating coil manufacturing.
  • Variability in coil height is eliminated.
  • Bobbins with terminals minimize material handling errors
• Micro-coil bobbins require wall thickness of at least .010”-.015”.
• Bobbin flanges with terminals need to be at least .050” thick.
• Micro-coil bobbins are usually made from liquid crystal polymer- see technical data sheets

Self supporting coils
Magnet wire selection

• Bondable magnet wire is wound on a mandrel where the magnet wire will bond to itself using heat or chemicals.
• Coil winding process can be designed to either bond on to a ferrite mandrel or be removed from a steel or titanium mandrel.
• Selection of magnet wire
  • Insulation coat- See NEMA literature- Common Thermal classes 150C, 180C, 200C. limited availability of 220C
  • Bond coat over insulation coat. Bonding agent will be activated 20-100C below insulation coat.
  • The coil operating temperature range will affect the bond coat selection. Bondable wire will soften in the field when subjected to bonding temperatures- see technical data sheets

Coils with special angles

• Avoid sharp angles- Round ID are easier to make than rectangular.
• Coils are wound flat but can be shaped using bondable magnet wire. Shaping process must preserve the integrity of the insulation coat.

Stripping fine wire
150-180 C vs. 200-220 C magnet

• Insulation coating with thermal ratings above 180C require additional process before tinning the leads
• Magnet wire finer than 46 AWG requires special tinning process because the wire cannot break the surface tension of the solder pot.

What affects inductance

• Inductance is the most common electrical measurement in Micro-Coils.
• Given the same wire size and number of turns, inductance will vary
  • Consistencies of core material
  • Consistencies of winding layers
  • Consistencies of bonding agent