ELFORM HEAT SEAL CONNECTOR BONDING PARAMETERS

 

A. Bonding Equipment.

  1. Bonding Equipment must be capable of applying a constant pressure by mechanical or pneumatic means. The heated bonding blade must be flat. Beryllium Copper is the most suitable metal. Silicone Rubber, 0.30mm to 0.45mm thick should be placed under the bonding blade during bonding. Sarcon TR is recommended.
  2. The machine set temperature can vary depending on the equipment and type and the substrate being bonded. The set point of the machine should be determined by measuring the internal temperature of the adhesive.
  3. The jig which holds the substrate can be made of either metal or phenolic, but the area directly below the bond area should not be thermally conductive.

B. Bonding Parameters.

  1. Bonding Temperature defines when the thermoplastic adhesive has reached the optimum flow temperature. 


 

Bonding Pressure

30 ~ 40 kg/cm2

Bonding Period

5 ~ 7s above 140C

Bonding Temperature

140 ~ 160 C

Silicone Rubber Hardness

70 ~ 80

Silicone Rubber Thickness

0.30 ~ 0.45mm

 

  1. Substrate conditions.

LCDs: Indium Tin Oxide traces on glass are most commonly used. Clean with an applicator soaked in ethanol. If the LCD manufacturer used a silicon zebra strip to functionally test the LCD there is a good possibility that a silicone residue is on the glass. This condition may be recognized by checking if water beads on the glass. Only a plasma etch can remove the silicone. Consult with your LCD supplier. Some suppliers of elastomeric connectors also have a type of compression connector that uses a flex circuit wrapped around a rubber core.  This type should be used for testing.

PCBs: Au, Sn or Carbon ink are recommended. Any metal that has non-conductive oxidizing properties is not recommended, e.g. Pb-Sn (unless Pb content is less than 10%). Check area for foreign particles.

C. Notes on Bonding

  1. Check co-planarity between substrate and the bonding blade with Fuji Low Pressure grade Prescale Film.
  2. Avoid touching the Heat Seal Connector (HSC) and substrate terminal area.
  3. If the PCB or TAB electrodes are thicker than 40 microns, double check adhesive transfer and bond strength.
  4. The bonding area on the substrate must be at least 15mm wide. A depth of at least 2mm is recommended.
  5. The bonding blade must contact over the substrate away from the edge, otherwise trace shearing may occur causing an electrical open.
  6. Bonding operations on the LCD and PCB are typically done separately, unless two independently driven bonding heads are used to assure one substrate does not act as a spacer to the other.
  7. Air bubbles can break out in the adhesive if the bonding temperature exceeds 185 C.  The bond will be unstable if this happens.
  8. On all types of HSCs, the bonding temperature should not be exceeded by more than 20 C. Otherwise adhesive will be squeezed away and the bond will be weakened.
  9. HSCs can be tacked into place before final bonding by touching them with a soldering iron set at 160C.
  10. The bond is permanent, but if the HSC is peeled off it will not damage the traces on the glass or printed circuit board. The conductive ink and adhesive residue may be removed by using acetone or MEK.
  11. Bonding quality should be judged after bonding to glass and performing a vertical peel strength test. All of the adhesive and 70% of conductive ink should be transferred to the glass.

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