Hi Eli,
Ever heard of the 'bimetallic strip' effect?
That top-to-bottom delta-T will cause warping; that was bad enough with SnPb but has much worse effects with the EU-RoHS-mandated Pb-free solders.
The possible consequences are pad cratering, foil/resin interfacial failure, trace fracture, head-on-pillow SJs.

Werner
Future workshops:
Pb-Free Soldering Processes: Survival, Quality, Reliability—PROBLEMS & SOLUTIONS, March 3, IPC/JEDEC Santa Clara, CA
Solder Joint Reliability: Part 1—Solder Joint Reliability Fundamentals, March 29, IPC EXPO/APEX Las Vegas
Pb-Free Soldering Processes: Survival, Quality, Reliability: PROBLEMS & SOLUTIONS, March 30, IPC EXPO/APEX Las Vegas



 


 

-----Original Message-----
From: Eli Sarig <[log in to unmask]>
To: [log in to unmask]
Sent: Tue, 6 Jan 2009 2:16 pm
Subject: [TN] Question about bottom heaters of reflow oven










Hi all,

My question is related to the necessity of down heaters in the reflow oven.
When we solder double sided boards, we *can* create a suitable reflow
profile using *only* the top heaters of the oven.
In that case, the bottom heaters remain at room temperature. We measure
almost the same temperature on top and bottom of the board.
Are there any limitations or problems that might happen using this kind of
process?

Thanks,

Eli.

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