Lifted pads, we all get them and have all had them at some point. But there are ways to prevent them from happening. A few of the possible causes for lifted pads will be discussed. There are several possible causes but we will focus on the most common. We refer to it as the IPC technique. The IPC is actually a company that sets the standards in proper reworking and electronic repair, we promise we did not choose IPC intentionally it sort of just landed that way.
Using generic, outdated and general profiles is probably the top reason for causing lifted pads. Generic profiles are those that you found scouring the internet available freely and sometimes paid for. Some of these are from PROFESSIONAL rework technicians that have a 95% success rate. While their success rate is not in dispute, using their profile as your own is definitely a huge problem. Profiles can not be shared, its a simple concept but apparently not widely known. Reworking is about temperature, which a profile basically is. A technician in Hawaii certainly can not use the same profile as a technician in Alaska. While this is an extreme scenario it proves the point that the temperature differences in those locations are at opposite ends of the scale.
Profile development is something many new rework technicians fear, but is the only way to achieve flawless results. While that profile you got from a friend, paid for or found online will not work the same way as it did for them for you it can be used as a starting point or base for testing. In order to properly develop a profile you need to take into consideration ambient temperature, humidity level, air flow, machine power, machine size, and brand of flux.
As with anything in life proper preparation is the key to success. Going for a job interview, getting married or starting a business require preparation, while all of them can be achieved by simply winging it, the results will always vary quite differently and sometimes end in disaster. The same principle applies with reworking. While you may have success with reworking or only get lifted pads on about 30% of boards, finding a way to offer clients the best repair possible should be on the top of any technicians list.
Pre bake helps tackle the problem of moisture found in printed circuit boards. Moisture becomes trapped in the layers of the board and components and can cause several issues such as delamination, pop corn and of course lifted pads. Moisture is essentially water inside an electronic device, and we all know water and electronics dont mix. By performing a pre bake of the board, this is where the pre comes in, and means before you rework you can help set free that trapped moisture and allow it to move on to greater pastures or at least out of your way.
After removal of the component, site cleaning is the next step. Site cleaning refers to the left over solder that is on the bga pads and is preventing you from placing a chip on them. This is a critical step and will determine whether or not you will have to perform pad repair. Delicate strokes of the soldering iron tinned with lead solder help remove the old lead free solder by lowering the overall melting point. Gently scraping the solder away with the aid of flux helps with the oxidation problem. After this delicate process, desoldering braid is used to further remove any residual leftover solder, followed by an alcohol rinse or ultrasonic bath the board is now ready.
The problems that occur during this step are primarily improper operator training. The technician must be extremely gentle as the pads are in a fragile state as they have already gone through some heat cycles and degradation is imminent. The proper tools are essential as is proper technique of the technician. The use of a high wattage soldering station and wide flat tip are required for proper results.
Article collaboration with XModdz