Converting Tin/Lead BGA Pads to Gold Plated

Figure 1: Solder covered BGA pads afer component removal.

When engineers are developing or upgrading products, the focus of their manipulations can often involve a BGA device.

We commonly receive requests to dismantle a socketed BGA and place the BGA component directly on the circuit board surface. We also receive requests to migrate a soldered component into a socket arrangement.

The challenge with a rework that involves the removal of a soldered BGA to install a socket in it's place is that most often the pads on the circuit board surface will need to be gold plated. In this case all 1000+ pads needed to be gold plated. That, my friends, is a piece of work. 

Figure 2: Conductive ink applied on the bottom side vias of circuit board to provide a conductive path for plating.

 

In Figure 1 you see the soldered pads were the BGA component was originally located.

In order to reliably plate any conductive surface you must establish an electrical connection. How do you make an electrical connection to 1000+ pads? How do you prevent the stripping and plating chemicals from contaminating the circuit board? 

For this rework project the BGA pads were all connected to plated through hole vias, and each via connected through to the opposite side of the circuit board. 

The rework procedure follows. First a dissolvable conductive ink was applied to the underside of the board covering all the required BGA vias. The ink was then cured.

Figure 3: Solder removed and pads plated with gold.

A buss wire was connected to the conductive ink area and the opposite end of the buss wire was connected to the cathode of the plating unit. Plating tape and removable, non-permanent mask were used to isolate the plating surface and to provide a pathway for the excess plating solutions.

The solder stripping and plating steps were the easiest part of this rework. Preparation and clean-up are the steps that require the most care, and the most time. Once the gold plating was completed and the area was given a very thorough inspection,  the dissovable conductive ink and plating tape were removed.

Figure 3 shows the completed and gold plated 1000+ pads. Easy as 123 and 456789......

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