Elform Heat Seal Connector Design Guidelines



This document gives the design rules and discusses the technical issues involved in designing a custom Heat Seal Connector. Accurate drawings are essential for a successful application.

Heat Seal Connectors are made by screen printing PTF conductive ink onto a PET base film. The traces are covered with a layer of thermoplastic electrically anisotropic adhesive which is loaded with gold plated nickel particles.   

The first decision you will have to make is what type of Polymer Thick Film (PTF) ink is required. The resistance of graphite PTF ink is 50Ω /square and silver PTF ink has a resistance of 0.2Ω /square. The maximum power dissipation of any type is 100mW and the resistance of the trace is calculated by the following formula:
 
 R = Ω /square x (Trace Length / Trace Width)
 
 A silver trace 10mm long and 0.5mm wide would have a resistance of 4Ω and could carry 160mA of current. Anytime silver is used, a gap of 0.5mm is left between the ends of the traces and the edge of the connector. This prevents silver migration. Be sure your drawing includes this. 

Once you have determined the type of ink suitable, the dimensions of the Heat Seal Connector must be defined. The width (W) of your Heat Seal Connector will be a function of the required pitch (P) and the number of conductors (N). Conductive traces may not run along the edge of the connector. This has to do with the die-cut tool tolerance among other things. The spacing between the edge of the connector and the center-line of the edge traces is referred to as dimension A. 2.0mm is the minimum recommended for dimension A. The reasoning behind this is enough adhesive is along the ends. The formula for determining the width of your connector is W = (2 x A) + ((N-1) x P). Dimensional tolerances are shown below. Trace edges may be 0.5mm from edge away from bond areas.
 
The length (L) of your Heat Seal Connector is generally defined by the package. Don't make the connector too short as to cause handling difficulties, or too long which would lessen the yield and drive up the cost. To avoid yield problems an HSC with a pitch below 0.40mm pitch should be limited to 80mm(W) x 40mm(L).  The minimum dimensions for any pitch are 5mm(W) x 8mm(L).
 
The ink side of your Heat Seal Connector may be protected with either a printed UV cure insulation or a layer of PET Film Lamination (FL). UV cure insulation has a tolerance of 0.2mm. FL has a 0.8mm tolerance. The bond area (dimension I) for UV cure should be 2.0mm or more, 3.0mm or more for FL (FL needs a minimum length of 10mm). FL requires an additional set of tooling to make the blanking sheets, but it is the only choice for hard creasing or to prevent shorting if your HSC will contact a metal surface. UV cure causes only a slight increase in the screen charge. 
 

The lowest cost shape for a heat seal connector is rectangular. Yutek uses Thompson steel rule dies mounted in laser cut ABS plastic to cut out parts. Die-cut tool pricing increases with additional aspects. The number of apertures also has an effect. All aspects must be defined dimensionally so that Die-Cut Tools may be made. Radii may be put on inside corners. The minimum radius is 0.6mm. Chamfers are more expensive than radiuses. Die cut holes may be put in a connector for assembly purposes. The minimum diameter is 1.2mm.  Slots may be cut a minimum of 2.0mm from the end of the connector. Slots may have a minimum radius of 0.7mm and must be a minimum of 0.5mm away from the edge of a trace. A slot is typically used opposite a hole for fine adjustments. It is very important that drawings specify which side is the ink or non-ink side. Drawings cannot be accepted without this note.   

 

 

Design & Physical Parameters

 

Pitch < 1.0

Pitch > 1.0

W

0.25

0.25

L

0.25

0.25

B < 100

0.05

0.1

100 < B < 150

0.06

0.1

B < 150

0.07

0.1

D

0.20

0.20

P

0.05

0.07

A

0.2

0.2

G

0.2

0.2

F

0.3

0.3

E1/E2

0.05

0.1

H (min, 1.2)

0.15

0.15

K (min, 0.5)

 

 

J (min, 1.0)

 

 

I (printed)

0.2

0.2

I (film)

0.8

0.8


 
Alignment traces are commonly used when the pitch is less than 0.7mm, since at that pitch alignment holes are no longer effective. Alignment traces have no effect on tooling costs. One type of fiduciary is the dummy alignment trace (below left). Traces with silver must be stopped 0.5mm from the edge, so dummy traces printed in each corner of the bond areas are aligned to the traces on the substrate. Sometimes a horizontal line is brought out the edge to form a "T". Another method is to print a cross hair on each corner of the bond area.
 

If you use a CAD (we use AutoCAD 2002) program you can attach the DWG or DXF file to an Email message (our address is sales@elform.com).

 

HOME