Reverse Spike

Having the last two zones at the reflow temp (spike) is typically done on long ovens (10 zone) running at high conveyor speeds. This enables you to achieve peak temp and TAL as per the solderpaste specs at high production rates. Concerning reverse spike, please note Marc Apell's (reflow soldering engineer at Speedline Technologies- Electrovert) comments:

Lead-Free Reflow Profile Requirements: Due to the higher melting points of lead-free solder formulations, the profiling requirements will change a bit, thus requiring some changes in the setup of the reflow equipment. A change that is commonly overlooked is a �flatter� profile during the reflow of the solder. Due to the tighter process window, the peak temperature and TAL must be achieved without overheating the assembly or components. This requires a longer reflow zone and the ability to effectively transfer heat to the product. The issues can be solved by using two zones for the reflow requirement, or perhaps using a reverse spike in the reflow zone. With this method, the second to last heating zone maintains a process temperature higher than the last zone to drive heat into the product quicker. Then the final zone is used to sustain a uniform temperature in the assembly.

This can apply to Sn/Pb profiling as well.

For Marc's entire paper, please go to this link:

www.speedlinetech.com/docs/ Lead-Free-Reflow-Considerations.pdf

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