my concern would be the properties of the potting, not the solder joints. 
Elevated cure may result in a higher potting Tg than room temp cure which 
can affect the low temp cycling performance of the potting. Something to 
think about if you have a choice. We pot products for harsh environments. 
If you are not worried about -40 or +125C you have less to worry about. 

CTE mismatch between potting/boards/components can definitely cause 
failures and fracture solder joints. Make sure you understand the potting 
properties for the temperature range, and I would run strain gages during 
temp cycling to verify.  We often find some of this potting data you need 
is not included in the datasheets. Work with the potting manufacturer. 
Harder pottings can work, but CTE mismatch is more of a concern and needs 
to be tested to make sure it will work for your product spec.

The smaller the potting volume also reduces these risks. Most issues we 
see are with larger products and not small sensors.



Roger Mack  P.Eng. 
Manufacturing Specialist
Parker Hannifin Electronic Controls
Electronic Controls Division
1305 Clarence Avenue
Winnipeg, MB  R3T 1T4 Canada 
direct 204 453 3339 x373
[log in to unmask]
www.parker.com/ecd







From:   Phil Bavaro <[log in to unmask]>
To:     <[log in to unmask]>
Date:   07-08-2014 02:04 PM
Subject:        [TN] High cure temp for potting electronics
Sent by:        TechNet <[log in to unmask]>



I was asked for my input on a design where the engineers want to fully pot 
some rigid flex pwbs with a thermal potting material that requires a cure 
cycle of 150C for two hours and cures to a Shore D hardness of 80.

My immediate reaction was to voice concerns over intermetallic grain 
structure growth but thought that I should reach out to this group of 
experts before responding.

We are using Sn63Pb37 solder.  The PWAs are full of reflow oven compatible 
components.  We normally do not expose our PWAs to any cure cycle 
temperatures over 110C.

Does this elevated cure cycle lower the reliability of the solder joints 
(more brittle)?

Will the extreme hardness of the material cause mechanical stress on the 
components?

Any help is appreciated.

Phil
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