Hot air reflow is used for faster profiles, especially desirous when there is a great volume of BGA rework to be accomplished. IR reflow is preferred for micro miniature devices as the lack of air flow prevent the component from being disturbed during reflow. That is, the viscoplastic material property of solder ball is ignored, the reflow profile is simplified and the accurate heat capacity is not considered. If the PCB is bowed or warped, they might not be able to properly fit into the final assembly or opens may be formed.īGA rework reflow sources commonly used include both hot air as well as infrared heat sources. The bowing can be exacerbated by the proximity of other components such as pin-in-hole connectors that may anchor the PCB, thereby enhancing the localized bowing under the BGA. This can be a serious problem in the case of very thin PCBs or boards with an uneven thermal mass distribution. Below in Figure 1 is an example of an Alpha OM-353 / SAC 305 Lead Free profile graph. The solder paste manufacturer will base the profile on the specific alloy and type of flux. The most common are solder paste and component manufacturers. PCB warping and bowing should be minimized by the BGA rework process. There are several sources for how a reflow profile graph should look like. Cleaning parameters should those be used in the original assembly process. If a water-soluble paste is used, the reworked area needs to be cleaned. The solder joint between the ball and the PCB pad should be similar in size and shape to the ball/part joint. Care should also be taken to not overheat any internal thermal grease if the BGA is capped.Īfter successfully attaching the BGA to the PCB, and allowing the board to be cooled down, the perimeter row of solder joints should be visually examined. This care must be extended to components with low melting points such as connectors or standoffs or adjacent moisture-sensitive devices. Solder alloys play a pivotal role in surface mount technology (SMT). In addition, care must be taken to ensure that adjacent components are not damaged during the reflow process. Ensure dwell time above reflow as per the solder paste manufacturer's specifications.Time 25☌ to peak temperature 6 minutes max. All joints to be in the solder manufacturer's specified reflow range 20 seconds 30 seconds Ramp-down rate (Tp to TL) 6☌/second max.Minimum joining temperature high enough to ensure good wettability.Peak joint temperature to minimize Pb dissolution.Lead-free Reflow Profile: Soaking type vs.Reflow oven zone temperature set up and thermal profile Here is my attempt at an SMD Solder Reflow station.Save optimized parameters as per the target board’s reflow specification.Adjust the parameter setup and test several times to find the upper limit and bottom line of the real-time reflow profile.Compare real-time thermal data with the virtual profile.Burn-in a test board with thermal shock and mechanical shock to check the board’s reliability. Synchronising Reflow->PC Profile Name Profile settings Zone temperature, hold time, active or not Extraction hood.Check the solder joint quality, PCB and component status.
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