Any tips for MCU breaking after reflow soldering?

Thread Starter


Joined Nov 7, 2022
After soldering up the parts, the DMA process on my MCU's (ATSAML21J18B-AUT) is breaking. I use an IR oven (T962A), cover the MCU in a heat shield, and reflow using low temp solder (the process gets up to 180C). With an iron at 200C, I will touch up pins with bad solder joints. The MCU is rated for a reflow process temperature up to 260C. However, I had 0% yield when reflowing at this temperature, and a very low yield when out-sourcing the build to someone using this temperature process.

The problem is that the CPU and most functions work great, but the DMA handler can’t be able to load data in from the ADC. The DMA process works great on a solder-less fixture and I check the parts prior to assembly.

I do everything on ESD mats and avoid handling the parts. My yield is around 30-50% of boards currently.

Has anyone had tips for things to check out? Thanks!


Joined Aug 7, 2020
I suspect you have one or more pins not soldered.
When you touch up the soldering on the pins with a soldering iron, use some flux.
I solder microcontrollers with lead-free solder with hot air at 350°C and have no problems (except with the occasional unsoldered or shorted pins), provided I let it cool down before powering it up.


Joined Jan 23, 2014
Are those genuine new parts purchased direct or from an authorized distributor? I see they are currently backordered until next summer at the earliest.