Thx. There is not enough of mfg trick to compensate half hearted design. As old say indicated.
--------------------------
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________________________________
From: Werner Engelmaier <[log in to unmask]>
To: Joyce Koo; [log in to unmask] <[log in to unmask]>
Sent: Tue Mar 02 07:08:30 2010
Subject: Re: [TN] BTC rework, Square SJs
Hi Joyce,
The ball collapse comes from the combination of package weight, choice of paste, solder alloy, surface tension, amount of paste:pad area, extension of pad beyond package, but has little to do with reflow profile [provided it is adequate]---so 'finger-pointing' is misplaced---it is the design details in almost all cases.
By the way, there are non-collapsing balls available for Pb-free as well---they are just not made of solder.
Werner
-----Original Message-----
From: Joyce Koo <[log in to unmask]>
To: [log in to unmask]; [log in to unmask]
Sent: Mon, Mar 1, 2010 11:58 pm
Subject: Re: [TN] BTC rework, Square SJs
I am looking for a way to differentiate poor process (bad reflow profile) vs bad
design. If, say 5% - 20% collapse should be achieved by reflow, anything else,
such as cte mismatch or pcb warpage would attributed to the bad design (I.e. Un
balensed board, selected wrong pcb material) if such acceptable guideline can
not be established, it would be a finger pointing game. As much as I like the
computer game (hehehe), but not any "finger pointing" type. ,
--------------------------
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----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Mon Mar 01 23:31:01 2010
Subject: Re: [TN] BTC rework, Square SJs
Hi Joyce,
No such valid shortcut--why not do the analysis? Or better yet, hire me.
Maybe it is time for Bev to bring me up for a workshop.
But it is really not that difficult.
Werner
-----Original Message-----
From: Joyce Koo <[log in to unmask]>
To: [log in to unmask]; [log in to unmask]
Sent: Mon, Mar 1, 2010 11:09 pm
Subject: Re: [TN] BTC rework, Square SJs
Werner,
Thx for the reply. However, the old Pb rich ball solder to the board using
eutectic can be ensure the proper stand off achieved. At current lead free,
there is a little attention being paid to achieve the proper standoffs. As for
the good workmanship and process, regardless the size and cte mismatch, should
ipc establish a proper guideline, if not spec for establish % collapse of ball
standoff requirements? Rather than depends upon individual case of cte, parts?
I have seen some squarches bga joints almost look like LGAs. Sure it is not
"good". Can't wait for rel data to establish each of them. Can so guru come
out a number that universally acceptable? At least meet the "intend of the
design" in term of reliability. Any takers?
--------------------------
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----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Mon Mar 01 19:09:37 2010
Subject: Re: [TN] BTC rework, Square SJs
Joyce,
That depends on the reliability you want to achieve, the package size, the
delta-CTE and the cyclic delta-T.
Werner
Upcoming workshops:
May 21, IPC Int. Conference on Reliability and Quality of Lead-Free Electronics,
Frankfurt, Germany,
“Reliability Issues and Solution Options for Pb-Free Soldered Electronic
Products”
May 26, FED Seminar, Stuttgart, Germany,
“Bleifreie Lötprozesse—Frühausfälle, Qualität, Zuverlässigkeit”
June 8, SMT/HYBRID/PACKAGING 2010, Nürnberg, Germany,
“Reliability Issues with Lead-Free Soldering”
-----Original Message-----
From: Joyce Koo <[log in to unmask]>
To: [log in to unmask]
Sent: Mon, Mar 1, 2010 6:09 pm
Subject: Re: [TN] BTC rework, Square SJs
Warner,
What is the max collapse allowable of ball from its height?
--------------------------
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----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Mon Mar 01 13:56:14 2010
Subject: Re: [TN] BTC rework, Square SJs
Hi Chris,
The problem with this SJ is the low solder joint height 9=reduced reliability)
and the stress concentration geometry from SMD.
Werner
-----Original Message-----
From: Chris Mahanna <[log in to unmask]>
To: Werner Engelmaier <[log in to unmask]>; [log in to unmask] <[log in to unmask]>
Sent: Mon, Mar 1, 2010 1:08 pm
Subject: RE: [TN] BTC rework, Square SJs
In cross section, the vertical sides of the joint are straight. I assume it has
more/less retained the shape of the [trapezoidal?] stencil.
Chris
From: Werner Engelmaier[mailto:[log in to unmask] <mailto:[log in to unmask]> ]
Sent: Monday, March 01, 2010 12:52 PM
To: [log in to unmask]; Chris Mahanna
Subject: Re: [TN] BTC rework, Square SJs
Chris,
What do you mean by "squarejoints?"
Werner
-----Original Message-----
From: Chris Mahanna <[log in to unmask]>
To: [log in to unmask]
Sent: Mon, Mar 1, 2010 12:15 pm
Subject: [TN] BTC rework, Square SJs
Are square joints simply due to the small mass of the components, or is it
possibly an indicator of insufficient heat? We have no indication that any of
the paste didn't flow. Wetting looks good. All evidence is from microsection.
Thanks,
Chris
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