BGA Package Replacement Procedure
Steps in BGA package replacement
Removal of the BGA packages/ component from PCB would be the main step. Proper cleaning of the site pads comes next. Applying fresh lead or lead free solder balls to the chip or reballing followed by reworking the BGA by heating it back the PCB completes the replacement.
The Ball Grid Array package has been used for a long time in SMT PCB designs. The reason to use BGAs mainly to decrease overall size and most importantly for the increased performance. Other reasons include planned obsolescence as well as a sturdier build. With many consumers upgrading desktops and laptops using the same base system there is no benefit to the manufacturer. By creating a product that can not be upgraded as easily this forces consumers to purchase the next model. However using this technology in products that may be used in harsh environments is a large benefit as the chips are essentially stuck in place and risk of them coming loose is impossible due to drops. The BGA package can be found in many of the Rugged products including Panasonic Toughbooks, and recently Intel has decided to move its chipset line to the BGA type package.
For Component Removal
With things becoming more and more complicated in design, there are certain things that should be understood without a doubt before performing rework in order to remove the BGA package. Some essentials before removal would have to include the PCB baking or preheating. This takes care of saturation of the copper from the PCB, you would then apply top heater to a target package or component that will be lifted, this acheives having heat localized at only the package/ component area and not having distribution around the thermal conductive type material of a PCB or surrounding components.
Temperature monitoring of the package using thermocouples or TCs is a must, Omegas in this case are very popular due to consistent temperature monitoring. As always during heating of the component using the top heater, the heat generated needs to be local to that area while the solder becomes liquid. It must remain in a liquid state for a set period of time to ensure each individual solder ball is in fact in a liquid state at which point we can remove the component or package from the PCB using suction or vacuum.
However, if the PCB not been preheated properly or full saturation has not occurred, then heat being produced from the heaters will be processed throughout the board until all of the copper has been completely saturated. Usually when this occurs, a package or component could potentially turn into unsalvageable part rendering the need for an expensive part. Some scenarios include; dies going past the max suggested temperature; temperature differences from PCB and BGA goes beyond the limits thus resulting in discoloration and delamination; all of the heat coming from the top heater to turn the solder liquid starts to affect other surrounding parts; as well as dimishing the flux benefits since activation has passed. Proper baking is integral in keeping composition of the board or the BGA. This is why profile development and proper use of TCs is crucial in reworking. Temperature is a key factor in reworking and having the proper equipment and procedures will increase reworking success.
Most IR heating rework staions require less build parts then Hot Air, due to the way they operate. There are both pros and cons in this technology. Hot Air technology, have several nozzles for the many BGA sizes. There is a benefit to this since you can adjust the air from the nozzles when heating. BGAs usually are darker on the top, except for the die in the BGA. Absorption and reflection needs to be considered with IR, usually with cheaper heaters the center puts out most of the heat and other areas are not as even. This is where having high quality heaters is crucial in order to minimize the problems with this technology as such we recommend Elstein.
Because of this Hot Air may seem to be a better option because of the absorpting of heat doesnt matter as much when color is involved such as darker or lighter. There is a huge benefit that Hot Air has if available and that is nitrogen. The atmosphere in reworking is best when there is no oxygen since oxidation will be on the solder as it becomes in a liquid state. With nitrogen being used there is no oxygen thus no oxidation.
BGA Site Cleaning
So now the component has been removed, there is left over solder balls and time to perform BGA site cleaning. This is usually done with the reworker using a high quality soldering iron such as Hakko FX or JBC and BGA desoldering braid. Since chances are it has lead free solder a higher melting point makes the process difficulty higher. Hot Air is not advised since; there is the possiblity of causing damage to solder mask because of excessive and less control of heat; and of course the increase of internal metallic layers or basically thicker PCBs.
Another method is using extremely expensive equipment, but things can be done much safer. This also reduces user error. BGA site cleaning requires a fixture of sorts to hold the the BGA, so solder can be moved without error. Pre heating or baking is still recommended, so the BGA will not be damaged thermally by too high rate of heating. When the lead or lead free solder is having heat applied and the solder becomes liquid, the nozzle from the vacuum starts to remove solder. This is unfortunately going to be another thermal cycle, therefore tips need to be made so that only a single quick pass is needed to remove all solder from the pads. Several passes increase chances for damaging the site and causes unnecessary heating for a longer period of time. Using fewer passes will keep the solder liquid for a short time.
To reduce costs, the chip is usually not discarded unless confirmed faulty after the removal. This is usually done through physical inspection and continuity tests. In order to apply fresh lead or lead free solder balls/ spheres and have them reflowed back to the BGA site, pads on the chip need to be fully cleaned of left over flux and old solder ball residue. There are severay ways of placing the balls. Most common is stencils that have holes for each solder ball aligned appropriately to match the chip. The application of a tacky flux noteably Kingbo Flux will help keep the solder balls in place on the pads while the excess are discarded and the stencil is removed.
At this point all that is required is for the solder balls to be reflowed with the proper thermal heating cycle. Having proper thermal profiles prevents possible excess movement of the solder balls which can result in bridging. Briding is where 2 or more solder balls join together to form a single ball. There are situations where the solder balls failed to attach or where some were not in place after removal of the stencil, manual ball rework will be used for placing single solder balls onto the device. In some rare cases, no matter how much flux or heat is used solder will not stick to the pad and this is generally caused by oxidation, the use of a fiberglass pen will remove the oxidized layer and allow the solder to melt onto the pad.
Component Attach/ Reflow
After the chip has been lifted cleaning of both sites, it is time to place the chip onto the board. This step is quite close to removing the chip package from the board. The obvious change is since the chip package is not on the board, is we have plenty of room to either paste solder onto the chip or board before it is soldered.
BGA reworking repair is much more complex than simply heating, removing and replacing a known defective device. While you can get away with this on smaller chips such as SMT, BGA is not as forgiving. With more maufacturers moving towards smaller PCBs, socketed design will eventually become obsolete. POP or Package on package is becoming more common and that is when there is another BGA along with solder balls on top of the main BGA package, an example of this is the RSX chip which has 4 memory modules using .2mm solder balls on top of the GPU itself. Keeping this in mind it is safe to assume that BGA technology will be come more advanced, and thus requires proper operator training, equipment and thermal profiles.