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Exactly.

C.W

#29730

Can excessive reflow(longer dwell time) cause open joint? | 29 July, 2004

hello, BGA was a little excessively reflowed with dwell time(above 183C - solder paste = 63/37) over 2 min, peak temp is 218C. I inspected the BGA under X-ray and there is a little voids but within the acceptable range, i then used the Ersascope to check for the perimeter joints, the wetting of the outer rows look good, i.e shinny and smooth joints were decernible. Same process parameters were used for 24 brds, Test yield is 70%, the other 30% of brds failed. Customer couldn't pin point the problem but they claim that the brd worked well before, so they insist the problem is coming from the reworked location, they said either is a bridge or open, but bridges is ruled out as the x-ray doesn't show any sign of bridging, but i do not know if the excessive reflow could be a problem that lead to open joints besides increase the growth of intermetallic. Any comments or recommendation? Thanks!!!!

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Bryan Sherh

#29732

Can excessive reflow(longer dwell time) cause open joint? | 29 July, 2004

Some short happens between the balls of CPU socket in my site.we decrease the reflow time from about 90sec to 50 sec and decreased the fail rate of short.but x-ray shows balls from part of the Ball array deformed....we can't further decrease the time above 183C and we think the root cause is that the weight of the socket...vertical force from upside make the balls deform...if you've Socket T in your process ,check your socket with X-ray after reflow. Thanks and best regards Bryan

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#29754

Can excessive reflow(longer dwell time) cause open joint? | 30 July, 2004

Excessive Time above Liquidus will cause a solder joint to become extremely brittle. Any shock or stress to the joint can lead to a failure.

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Francois Monette

#29768

Can excessive reflow(longer dwell time) cause open joint? | 30 July, 2004

A couple of other potential issues are moisture/reflow related issues. This can include internal delaminations inside the component, potentially breaking or lifting the wirebonds. It may also induce warpage where the corners of the BGA will curl up. In both cases you may get opens.

Do you know how much moisture was in their components in the first place ? Even if the components were still within their specificed floor life, the additional thermal excursion may cause the same types of defects.

For more information on moisture-related defects you can consult the MSD Knowledge Base on our web site at http://www.cogiscan.com.

Regards,

Francois Monette fmonette@cogiscan.com

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Rush Fan

#29838

Can excessive reflow(longer dwell time) cause open joint? | 4 August, 2004

I might suggest that you check with your solder paste manufacturer to see what is recommended for time over reflow. Typically, I think most are between 60 and 90 seconds over 183. Also, consider the rate of cooling. The faster you cool the solder, the smaller the grain structure which provides the strongest joint. Also, review the reflow soldering section of IPC-S-816, SMT Process Guideline and Checklist. That may give you some helpful tips.

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Carl

#30023

Exactly. | 13 August, 2004

Also, excessive time at reflow really begins to stress the substrate and components as well.

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