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From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Thu, 10 Nov 2016 22:15:10 +0000
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Not only is Dave correct, but here is another consideration many engineers overlook or fail to take into account when setting up a reflow profile:

They attach TCs to a scrap populated CCA (if they have one) or use the same profile as a very similar assembly. Both of those are good methods.

But the profile seen by a single CCA riding through the reflow oven, with no additional CCAs loading the chamber at the same time, is completely different than a profile seen by a single CCA.

So if you set up your profile using just one board (your thermocouple board) and you set it on the low side because you don't want to subject the production CCAs to any more heat than is necessary to get the job done, then during actual production you have perhaps 6 or 7 CCAs in the oven at the same time, none of them will see the desired temperature and time above solidus due to the oven loading. The quantity of ovens going through the reflow oven at any given time can have a huge impact on the temperatures seen by each board.

Consider that when setting up the initial profile and put perhaps two or three scrap CCAs in front of and behind your profile board so you see the worst-case production temperature and time above solidus.

dean



-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Blair Hogg

Sent: Thursday, November 10, 2016 2:49 PM

To: [log in to unmask]

Subject: Re: [TN] Reflow Profile using HASL or ENIG



Interesting, Dave. That seems to indicate that a profile that works fine for a HASL board may not work as well for a ENIG board as the solder doesn't have sufficient time above liquidus to create a bond with the nickel. Is my understanding correct?



Blair



On Thu, 10 Nov 2016 13:48:51 -0600, David Hillman <[log in to unmask]> wrote:



>Hi folks - lots of good comments, just one more to add: copper diffuses 

>faster than nickel so some folks increase their reflow temperatures 

>5-10C and/or slow down the belt speed 3-6 inches per minute. It isn't 

>necessary to do this but it does have some good metallurgical basis. 

>Werner Englemaier used to advocate doing this when a board finish 

>involved nickel (Werner and I discussed this at length, very fun 

>conversations). I set my reflow profile based on the board thermal 

>characteristics and the solder paste material but being aware of the 

>plating metallurgy impacts (such as the gold embrittlement Wayne detailed) is always a good idea.

>

>Dave Hillman

>Rockwell Collins

>[log in to unmask]

>


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