This has been shown in several studies on this topic to be LEASE effective type of heat shielding material. One of the most common-used but least-effective types of protection used is the Kapton ™ tape found in many areas of the SMT process. Protection from the heat sources, especially when using a hot air reflow source comes in many different flavors. In addition devices with underfill or components with TRV or glue around them should be watched and protected as these materials will become soft and potentially run all of the board making a large mess. This is especially tried when using a hot air source and for the device which is heat-sensitive including but not limited to ceramic capacitors, plastic connectors, batteries, and MELFs. Not only should the profile be correct and be confirmed through temperature measurements but the components in and around the BGA being reflowed need to be protected. Tin-lead solder should be above liquidus for a period of 30-45 seconds. Another “rule of thumb” for the reflow profile is making sure that for lead-free profiles the solder joint, as seen by the temperature in both corner and other balls, is above liquidus for a period of 60-90 seconds. The proper method for embedding these thermocouples is high-temperature epoxy for their attachment to the device or internal to the PCB. all in conjunction with learning about the thermal characteristics of the device and board during the reflow process. If there is the availability of a solder sample which allows the BGA technician to embed thermocouples into the solder balls (a corner, and 1 or 2 other places depending on the size of the package), into the die, around the BGA, near other components etc. Many times a BGA rework technician will use a standard profile in order to remove the device, tweaking or adjusting the profile based on the results achieved. One of the best ways to “learn” about the thermal characteristics of the PCB when there is only one PCB and there is not a profiling board available, is to use what is learned during the removal process to help “dial in” a reflow process. It is good to learn about the thermal characteristics of the PCB when trying to dial in a reflow process profile. There are several “rules of thumb” when zeroing in the process of reflow profile. Given the thermal mass of the board in and around the BGA the profile should match that of the replacement solder balls (if the device has been reballed and will be used a the replacement device) or match as closely as possible the profile of the device vendor's data sheet of the solder paste printed. The reflow process in BGA rework should emulate the manufacturing process as closely as possible. The replacement device is replaced using either flux or paste attachment. The reflow process occurs after the previous device has been removed and the site prepped. One of the most critical processes for BGA rework is the process of reflow.

Bga reflow temperature