At the EMPF, working with one-of-a-kind (or limited use) Ball Grid Array (BGA) devices is a common occurrence. The EMPF is frequently called upon to assist in BGA repair. One tool the EMPF uses is the Hepco Model 9000-1 BGA Solder Sphere Replacement System to repair damaged BGA devices. The EMPF utilizes this unit in its training classes, performing demonstrations in the Demonstration Factory, prototyping and assisting original equipment manufacturers (OEM) in repairing BGA devices. The Hepco Model 9000 is used on military as well as commercial BGA devices.

The Hepco Model 9000 operates using a self-contained vacuum system to secure the BGA component while transferring the desired pattern of solder spheres in a full array. Alignment is achieved through precision pins and specific tooling for ease of use, repeatability, and accuracy in sphere placement. Its repeatable process control will insure co-planarity and uniformity of the sphere's placement. The unit will accommodate virtually all BGA layouts and sphere sizes. A self-contained system, no additional air/vacuum is required.

During the last few years, BGA usage has increased dramatically among OEM. This is due, in part, to the increased complexity of electronics circuitry and higher demands placed on the industry by commercial and consumer customers.

The technology and process knowledge to effectively and efficiently repair BGA devices exists. An added attraction for BGA packages is that this technology is compatible with existing surface mount technology (SMT) assembly processes and equipment, so rework is fairly simple.

Preparing PCBs and Packages for Rework
Both the printed circuit board (PCB) and surface mount technology (SMT) devices, to be removed, are capable of absorbing moisture from ambient air. This may cause internal expansion and damage to the PCB and/or device during heating to the de-soldering temperature. Therefore, it is recommended to always bake PCBs and devices prior to any rework.

The recommended temperature depends on the maximum temperature that the devices on the PCB can withstand without damage. Generally, the allowed temperature is between 50°C and 80°C. Furthermore, a higher baking temperature requires a shorter bake-time.

At 50°C the recommended bake time is 48 hours.
At 60°C the recommended bake time is 36 hours.
At 70°C the recommended bake time is 24 hours.
At 80°C the recommended bake time is 20 hours.

Overheating & Warpage (Coplanarity)
PCB material is a mixture of fiberglass and resin, with copper tracks and vias, as well as a solder-resist coating on top. All of these materials expand at different rates during heating. If heating is unevenly applied, different sections of the same material will expand at different rates. This stress can lead to permanent distortion of the material. Warpage, as it is called, is usually a result of the buckling of the PCB. Warpage may make it impossible to solder a new device in the position where rework occurred, so the PCB is a reject.

During the process of component removal, a component can be damaged. For example, BGA solder spheres can be damaged and the expensive device destroyed.

• Place the component in the alignment plate
• Turn on the vacuum
• Remove residual solder and/or contaminates. (Always remove excess solder and clean the device. This can be done using solder braid. Then, clean off any dirty flux with flux cleaner)
• Print the flux on the component using the appropriate stencil
• Load the wand with solder spheres using the vacuum pick-up
• Align the wand using tooling pins
• Depress the foot pedal to release the full array of spheres
• Lift the block
• Remove the component from the carrier
• Reflow the part using the proper temperature profile.

Restoring BGA's that have been damaged during the manufacturing process or end-user handling, by performing a reballing process that restores the device to equivalent-to-new condition, can be a cost-effective process. This reballing process will provide substantial cost savings to the customer because it eliminates the high replacement cost for expensive BGA devices.

If you would like to see a demonstration of the Hepco Model 9000-1 BGA Solder Sphere Placement System, please call Jeff Stong at the EMPF. He can be reached at 610-362-1200 Extension 224 or at jstong@aciusa.org.