Operation On The Spot

Beyond the Standards

In the world of rework and repair there can never be a standard procedure for every emergency.  Things can happen too quickly and "on-the-spot" there can be an urgent  necessity to go above and beyond the recognized standards outlined in the IPC as well as other industry guides .  These kinds of situations demand innovation; new processes  that will provide reliable alternatives to scrapping out expensive, or critically needed printed circuit boards.  Through the years we've had many occasions to work closely with our customers and partners to create leading edge solutions. 

Below is an example of a recently developed procedure used to repair large surface with voids.  In this case we worked hand-in-hand with a customer who provided critical reliability data for the completed repair that confirmed the repair process to be sound.  Several challenging and unique approches were attempted before a final process was certified. Although this is a bit extreme, it does represent an example of the type relationship we have with many of our customers in developing new leading edge circuit board repair processes.

Process Specification

Document No. PRS1015

Conductor Repair, Surface Plane, Film Adhesive Method Written By A. Price Revision Pending ECN Number Pending Revision Date 12/15/2004 Outline This method is used to repair damaged circuit surface planes. The damaged areas are repaired with dry film epoxy, adhesive backed copper foil disks. They are bonded to the circuit board surface using a bonding press or bonding iron. References IPC-A-600 Acceptability of Printed Boards Special Tools/Materials Adhesive Backed Circuit Material Bonding System Epoxy Microscope Oven Precision Drill/Milling System Scraper Solder Soldering Iron Surface Mount Pad Repair Kit Instructions

1. Clean the area.

   Damaged Surface Plane

   
   
   
2. Secure the circuit to a Precision Drill/Milling System with a microscope available for viewing. Use an end mill slightly larger than the void in the surface plane and make a counter bore through the surface plane only. Do not mill into the laminate material, you may expose inner layer circuits.
   
   
3. NOTE
   Several adjacent counter bores may be required to fill larger areas.
   
   
4. Clean the area with solvent.
   
   
5. The area for the new Adhesive Backed Disk on the board surface must be smooth and flat. If internal fibers of the board are exposedor there are deep scratches in the surface they should be repaired. Refer to appropriate procedure.

   Figure 1: Milled area to remove damaged foil .

   
   
   
6. Select a replacement adhesive backed disk that matches the size of the end mill used to make the counter bore.
   NOTE
   The thickness should be selected to meet the requirements of the circuit board surface plane thickness.
   
   
7. With the adhesive backed disk positioned film side up, carefully scrape off the adhesive film from the outer 0.005" of the disk diameter.
   
   
8. Position the adhesive backed disk, film side down. Place a piece of Kapton tape over adhesive backed disk, position the adhesive backed disk into the counter bore. Press the adhesive backed disk into position. (See Figure 2).
   
   
9. Select a bonding tip with a shape to match the shape of the adhesive backed disk.

   Figure 2: Transplant new foil disk into milled out area.

   
   NOTE
   The bonding tip should be as small as possible but should completely cover the entire surface of the adhesive backed disk. Position the circuit board so that it is flat and stable. Gently place the hot bonding tip onto the Kapton tape covering the adhesive backed disk. Apply pressure and heat as recommended in the manual of the Repair System or Repair Kit for 5 seconds to tack the adhesive backed disk in place. Carefully peel off the tape.
   
   
10. Gently place the hot bonding tip directly onto the new adhesive backed disk. Apply pressure and heat as recommended in the manual of the Repair System or Repair Kit for an additional 30 seconds to fully bond the new adhesive backed disk. The new adhesive backed disk is fully cured. Carefully clean the area and inspect the new adhesive backed disk for alignment..

    Figure 3: Solder tin the area and blend in.

    
    NOTE
    Several adjacent counter bores may be required to fill larger areas.
    
    
11. Using flux and solder, carefully add a small amount of solder to a soldering iron with a "Blade" shaped tip, and flow solder over the repaired area.
    
    
12. Using the "Blade" shaped soldering tip and desolder braid, remove any excess solder Clean the area.
    
    
13. Using the Electric/Hand Eraser, clean and buff the soldered area to blend the repair to the circuit surface.
    
    
14. Using Kapton tape, mask off an area larger than the repaired area.
    
    
15. Using the abrasive pad, "lightly" buff the masked area to further blend the repair to the circuit surface as necessary. (See figure 3)
    
    
16. Clean the area.

Finish
Blend the surface type using an appropriate buffing material, such as: Scotch Bright, Kim Wipes, or Cotton Tipped Applicator. Matte and semi-gloss surfaces may require light abrasion in order to blend to original surface finish type. High gloss will require polishing with a Kim Wipe or a Cotton Tipped Applicator chucked in a Micro Drill System. Remove any loose particles as necessary and clean the area.

Evaluation
Visual examination and electrical tests as applicable.

Several members of the Circuit Technology Center team contributed to this feature story.