4.6.3 Edge Contact Repair/Rework, Plating Method

Printed Board Type: R/F/W/C
Skill Level: Advanced
Conformance Level: High
Revision: E
Revision Date: Jul 7, 2000

OUTLINE

Contaminated Gold Edge Contacts

This method is used to replate edge contacts by selective swab plating. Edge contacts may require replating if they become contaminated with solder or are scratched during handling. Other applications may arise when the plating on the edge contacts does not meet the minimum thickness specification or if the specification changes.

This electroplating process uses a DC power supply. One lead is connected to the connector edge contacts that need plating. A second lead is connected to the plating probe. The plating probe has an anode fastened to the tip. The anode has absorbent wrapping. The anode is dipped into high-speed proprietary plating solutions. When the saturated anode is swabbed across the circuit board connector edge contacts, the metal contained in the solution is plated wherever electrical contact is made. Prior to replating any solder contamination must be removed.

CAUTION
This method can be used to replate any metal surface including connector edge contacts, but it is essential that the surface to be plated is free of deep scratches, nicks, pin holes or other defects. If the edge contacts need to be replaced see appropriate procedure.

SAFETY
A thorough review of this method should be made before repairs are attempted. Technicians should become familiar with the tools included and should practice on scrap circuit boards.

To expect the best results a clean work environment is essential. A smooth work surface and good lighting are recommended. Safety glasses and safety gloves should always be worn when handling hazardous chemicals.

The work area should be adequately ventilated. It is particularly important to have adequate ventilation when using gold solution, since gold solution contains a very small percentage of free cyanide. If ventilation is not adequate, use a fan to move fumes away from the operator.

CAUTION
It is essential to follow the manufacturer's instruction supplied with the plating equipment.

ACCEPTABILITY REFERENCES
IPC-A-600 2.0	Externally Observable Characteristics
IPC-A-610 10.0	Laminate Conditions
PROCEDURE REFERENCE
1.0	Foreword
2.1	Handling Electronic Assemblies
2.2	Cleaning
IPC7721 4.6.3	Edge Contact Repair/Rework, Plating Method

Figure 1: Connector Edge Plating System.

TOOLS & MATERIALS
Abrasive Pad
Board Support
Cleaner
Conductive Pen
Desoldering Braid or Desoldering System
Eraser Stick
Flux, Liquid
Gloves, Antistatic
Gold Contact Plating System
Knife
Peel Testing Tape
Pin Fixtures
Plating Anodes
Plating Solution, Gold
Plating Probes
Plating Solution, Electroclean
Plating Cables
Plating Solution, Nickel
Plating Solution, Solder Strip
Plating Tape
Power Supply
Probe Clip
Rinse Tray
Rinse Bottle
Safety Glasses
Soldering Iron
Solder
Solution Swab
Solution Cups
Solution Tray
Tape, Kapton
Thickness Measuring System, Gold and Nickel
Water Sprayer
Wipes
Wire, Bus, 30 AWG
Work Sink

PREPARATION - Remove Solder Contamination

CAUTION
Safety glasses and safety gloves should always be worn when handling hazardous chemicals. Do not work within a small enclosed room without supplemental ventilation. If ventilation is not adequate, use a fan to move fumes away from the operator.

1. Figure 2: Flow solder over the entire surface of each contaminated contact.

   Clean the rework area.
   
   
2. Apply plating tape to the circuit board surface surrounding the area to be reworked. The plating tape will protect adjacent components and the circuit board surface from unwanted exposure to stripping and plating solutions.
   
   
3. Flow solder over the entire area of any contacts that have contamination using a soldering iron. This provides a more even surface when plating. Remove the bulk of the solder contamination using desoldering tools or desoldering braid. (See Figure 2).
   
   
4. Clean the area.
   
   
5. Place the circuit board on the board support so that the leading edge overhangs the rinse tray.
   
   

6. Figure 3: Swab the contaminated area with solder stripping solution until all solder has been removed.

   Swab the solder stripping solution over the solder contamination using a swab. Swab the surface until all remaining solder has been stripped off. (See Figure 3).
   
   
7. Thoroughly rinse the entire area with water. (See Figure 4).
   
   
8. Mildly buff the contacts using abrasive pad. Mild buffing will prepare the surface for plating and remove any remaining solder contamination.
   
   
9. Thoroughly rinse with water to remove any residue.
   

PREPARATION - Remove Poor Plating or Surface Defects

1. Clean the rework area.
   
   
2. Apply plating tape to the circuit board surface surrounding the area to be reworked. The plating tape will protect adjacent components and the circuit board surface from unwanted exposure to stripping and plating solutions.
   
   

3. Figure 4: Rinse the area with water. A water/air sprayer provides a full water flush.

   Clean the area.
   
   
4. Buff the contacts using an abrasive pad. Buff the contacts until all defective or poor plating is removed.
   
   
5. Burnish small scratches. Use the tip of the Tech-Pro Burnisher to work the copper material into the scratch and smooth out the area. Finish by mildly buffing the area to remove any minor burnishing marks. If there are large scratches the contact may need replacement. See Procedure Number 4.6.1 or 4.6.2.
   
   
6. Thoroughly rinse the entire area with water to remove any residue.

BUSING
A conductive bus must be made to all the contacts that need plating. There are 4 basic connection options.

NOTE
Making a reliable bus connection is the most important step in plating. All sorts of problems will be eliminated by taking the time to make a reliable bus connection.

BUSING - Wire Soldered to Edge (Option 1)

CAUTION
When finished, this method will leave a small unplated line along the inner tip of each contact.

1. Figure 5: Apply Kapton tape then solder a wire to the edge of the contacts needing plating.

   Apply Kapton tape to all the contacts to be plated. The High Temperature Tape should cover the entire contact except for a small line along the inboard edge. The Kapton tape will prevent further solder contamination.
   
   
2. Solder a wire directly to the inboard tip or connecting circuit of each contact to be plated. The smallest amount of solder should be used to prevent further contamination. (See Figure 5).
   

BUSING - Conductive Paint Applied to Edge (Option 2)

CAUTION
When finished, this method will leave a small unplated line along the inner tip of each contact.

1. Figure 6: Apply Kapton tape then apply conductive paint to the contacts that need plating.

   Apply Kapton tape to all the contacts to be plated. The High Temperature Tape should cover the entire contact except for a small line along the inboard edge. The Kapton tape will prevent the conductive paint from contaminating the contact surface.
   
   
2. Apply a thin coating of conductive paint directly to the inboard tip of each contact to be plated. The conductive paint should extend out to one edge so that a clip can be applied to make electrical connection. (See Figure 6).
   

BUSING - Mechanical Probe, Individual Contacts (Option 3)

1. Each contact needing plating can be individually probed using the plating probe. Touch the tip of the plating probe to the inboard edge of each contact or to the connecting circuit as each solution is applied during the plating process.

BUSING - Pin Fixture, Multiple Contacts (Option 4)

1. Figure 7: Sample plating anodes shown with fabric wrapping.

   Make a mechanical connection to each contact using a pin fixture. The pin fixture has spring loaded contact pins on centers matching the spacing of the edge contacts to be plated. The contact pins make direct mechanical connection to the inboard tip of each contact, the connecting circuit trace or a connecting plated through hole..

PROCEDURE - Plating Process

1. Place the circuit board on the board support so that the leading edge overhangs the rinse tray.
   
   
2. Make the cathode connection (-) to the circuit board by using a plating probe or probe clip. Connect the probe clip directly to the wire bus connection or to the edge where conductive paint has been applied. The cable should be connected to the (-) or black jack on the power supply.
   
   

3. Figure 8: Swab all the contacts by brushing the surface with the saturated plating probe.

   Connect the plating probe to the power supply (+) or red jack. (See Figure 7).
   
   
4. Set the output current on the power supply to setting recommended by the equipment manufacturer. Refer to Table 1 for general voltage/time settings.
   
   
5. Dip the plating probe into the electroclean plating solution. Wait a few seconds for the solution to saturate the absorbent wrapping.
   
   
6. Swab the entire surface to be plated by brushing the surface with the saturated plating probe. The plating probe should be moved back and forth briskly to prevent burning and to provide even coverage. (See Figure 8) Swab the area for the time recommended by the equipment manufacturer. Refer to Table 1 for general voltage/time settings.
   
   
7. Thoroughly rinse the entire area with water. Any burning or darkening of the contacts may be removed with an abrasive pad. Saturate the abrasive pad and the PC board surface with water and lightly buff the contacts until all evidence of the burning or discoloring is removed. Rinse the entire area with water.

   
   CAUTION
   Do not allow the rework area to dry out between steps. The water coating prevents oxidation.
   
   

8. Connect the nickel plating probe to the power supply (+) or red jack.
   
   
9. Set the output current on the power supply to setting recommended by the equipment manufacturer. Refer to Table 1 for general voltage/time settings.
   
   
10. Dip the plating probe into the nickel plating solution. Wait a few seconds for the solution to saturate the absorbent wrapping.
    
    
11. Swab the entire surface to be plated by brushing the surface with the saturated plating probe. The plating probe should be moved back and forth briskly to prevent burning and to provide even coverage. Swab the area for the time recommended by the equipment manufacturer. Before rinsing, lightly buff the contacts with an abrasive pad. Refer to Table 1 for general voltage/time settings.
    
    
12. Thoroughly rinse the entire area with water.
    
    
13. Connect the gold plating probe to the power supply (+) or red jack.
    
    
14. Set the output current on the power supply to setting recommended by the equipment manufacturer. Refer to Table 1 for general voltage/time settings.
    
    
15. Dip the plating probe into the gold plating solution. Wait a few seconds for the solution to saturate the absorbent wrapping.
    
    
16. Swab the entire surface to be plated by brushing the surface with the saturated plating probe. The plating probe should be moved back and forth briskly to prevent burning and to provide even coverage. Swab the area for the time recommended by the equipment manufacturer. Refer to Table 1 for general voltage/time settings.
    
    
17. Thoroughly rinse the entire area with water.
    
    
18. Remove and discard all plating tape and thoroughly rinse the area with water. Dry the area using a water/air sprayer or wipes.
    
    
19. Remove the wire or conductive paint used to bus the contacts.

    
    CAUTION
    Apply Kapton tape to protect the contacts from further contamination while removing the bus connection.
    
    

20. Thoroughly rinse the entire area with deionized water or rinse the circuit board in an aqueous water cleaning system.

Table 1
Typical Voltage/Time Settings

Surface Area	Electroclean		Nickel		Gold
	Volts	Time	Volts	Time	Volts	Time
<.01 in2	10.0 VDC	5 sec.	4.0 VDC	10 sec.	3.0 VDC	10 sec.
.01 - .05 in2	10.0 VDC	5 sec.	4.0 VDC	30 sec.	3.5 VDC	20 sec.
.05 - .10 in2	10.0 VDC	5 sec.	4.0 VDC	1.0 min.	4.0 VDC	30 sec.
.10 - .20 in2	10.0 VDC	10 sec.	4.0 VDC	2.0 min.	4.0 VDC	1.0 min.
.20 - .30 in2	10.0 VDC	10 sec.	4.0 VDC	2.5 min.	4.0 VDC	1.5 min.
.30 - .40 in2	10.0 VDC	10 sec.	4.0 VDC	3.0 min.	4.0 VDC	2.0 min.
.40 - .50 in2	10.0 VDC	20 sec.	4.0 VDC	4.0 min.	4.0 VDC	2.5 min.
.50 - .60 in2	10.0 VDC	20 sec.	5.0 VDC	5.0 min.	4.0 VDC	3.0 min.
.60 - .70 in2	10.0 VDC	20 sec.	6.0 VDC	6.0 min.	4.0 VDC	3.5 min.
.70 - .80 in2	10.0 VDC	30 sec.	6.0 VDC	7.0 min.	4.0 VDC	4.0 min.
.80 - .90 in2	10.0 VDC	30 sec.	6.0 VDC	7.5 min.	4.0 VDC	4.5 min.
.90 - 1.00 in2	10.0 VDC	30 sec.	6.0 VDC	8.0 min.	4.0 VDC	5.0 min.

Notes:

1. Surface Area is the total area being plated during each swab plating operation.
   
   
2. Voltage and Time setting shown in Table 1 are for a minimum of .000100" Nickel and .000050" Gold.
   
   
3. Settings are a guide. For precise thickness requirements the final thickness should be verified with proper measuring equipment.

EVALUATION

1. The rework area should be checked by measuring the thickness of the nickel and gold to make sure they meet the minimum thickness requirement.
   
   
2. The plating bond may also be checked by doing a peel test using peel testing tape.
   
   
3. Visually examine the rework area for color and luster.