BGA Rework and Reballing
Why BGA Rework Is Different
An area array package cannot be soldered with an iron. The joints are underneath the body, so the only way to make or break them is to heat the whole package until the alloy melts, using a machine that controls the temperature across the body and the board beneath it. That requirement turns a routine component replacement into a thermal process with a narrow window: too little heat and the joints do not reflow, too much and the board delaminates or a neighbouring component is disturbed. The equipment and the profile are therefore part of the process, not accessories to it.
Removal
Removal begins with heating the board from below to bring it to a uniform temperature and to reduce the local heat needed. The top side heater then raises the package to the point where the alloy melts, and the vacuum is applied to lift it clear in one motion. The critical parameters are the peak temperature at the joint, the time above liquidus and the rate at which the package is lifted, since lifting too early produces torn pads and lifted metal. The thermocouple for the profile is placed on the board surface beside the package or on the package itself, according to the machine’s procedure, because the machine’s own sensor does not see the joint.
Site Dressing
After removal the site has residual solder and flux, and it has to be returned to a flat, clean, solderable state. The methods are a wick with an iron, a vacuum with a heated nozzle, or a specialised site dressing tool, and each has its risks: a wick can lift a pad, a vacuum can leave the surface uneven, and a tool that is too hot can damage the laminate. The result should be inspected at magnification, and a site that has lost a pad or a land must be repaired before the new package is placed. Site dressing is the step where the most rework damage occurs, and it is the step that most rewards patience.
Reballing
Where the package will be reused, the old solder has to be removed from the package and new balls applied. The package is cleaned, a stencil or a preform is aligned, balls or paste are applied, and the assembly is reflowed so that the balls connect to the package lands. The alignment and the ball size must match the package, and the profile must be within the package’s own limits, which are often tighter than the board’s. Reballing is a skill operation with a real failure rate, so the economics should be considered: reusing a package saves the part cost but carries the risk of a latent defect and consumes time.
The Reflow Profile for Rework
The profile for rework follows the same logic as a production profile, with the peak above the alloy’s liquidus by a margin and a limited time above liquidus, but the geometry is different because the heat is applied locally rather than to the whole assembly. The board must be preheated to reduce the thermal gradient and to protect the laminate, and the cooling must be controlled so that the joint solidifies with a sound structure. Different nozzle sizes change the heat transfer, so the profile is specific to the machine, the nozzle and the board, and it should be developed rather than copied.
Verification After Rework
A reworked package cannot be inspected optically, so verification relies on X-ray, on electrical test and on the connections around the package. The X-ray shows the ball pattern, the bridges, the missing balls and the gross voids, but it cannot prove that every joint has wetted. The electrical test is the practical confirmation, and it should cover the nets the package connects to. Where the rework is on a high value or safety related assembly, the acceptance criteria should be agreed in advance, since a reworked package has a different reliability history from a new one and the customer may require that it be declared.
When Rework Should Not Be Attempted
The moment to decline a rework is decided before the heat is applied. A board that has already been reworked, a laminate that is moisture loaded, a package that is at its thermal limit, or a site where the neighbouring components cannot tolerate the temperature are all reasons to consider scrapping the assembly instead. The cost of a failed rework is not only the package and the time; it is the risk that a partially damaged board passes test and fails in the field. A written rule that states when rework is permitted removes that decision from the moment of pressure.
Training and the Skill Element
BGA rework is one of the few operations in a modern assembly line where the outcome depends heavily on operator skill. The machine controls the thermal profile, but the alignment, the site dressing, the ball placement and the judgement about when to stop are human. That makes training and a defined qualification route important, and it makes the yield of the rework station a metric worth watching. A technician who has reworked the same package type many times will outperform one who has done a single demonstration, so the work is best concentrated in a small team rather than spread across a shift.
FAQ
Why can’t a BGA be soldered by hand? Because the joints are underneath the package, so the whole device must be heated to reflow them.
What is site dressing? Removing the residual solder and flux from the board after a package is lifted, to leave a flat, clean, solderable surface.
Is reballing worth it? Sometimes, but it is a skill operation with a failure rate, so the part cost saved should be weighed against the risk and the time.
How is a reworked BGA verified? By X-ray for the ball pattern and by electrical test for the nets, since optical inspection is impossible.
When should rework be refused? On a board already reworked, a moisture loaded laminate, a package at its thermal limit, or a site with heat sensitive neighbours.
Conclusion
BGA rework is a controlled thermal process, so use the machine, develop the profile and verify with X-ray and electrical test. Decline the work when the thermal budget has gone. Rework control belongs to quality management, the joints come from SMT PCB assembly, and the confirmation is part of PCBA testing. Rework policy for a new package is set during prototype PCB assembly in 2026.
