Sorry for the confusion: the 1st generation BGA got lead rich ball (Pb more tha 85%). You attach use eutectic solder to the PCB. The high Pb ball never completely melted. The standoff of the BGA is ensured due to the ball high temp materials used by design. Similar to the C4 joints made by 95% Pb.
--------------------------
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----- Original Message -----
From: vladimir Igoshev <[log in to unmask]>
To: TechNet E-Mail Forum <[log in to unmask]>; Joyce Koo
Sent: Mon Mar 01 23:30:48 2010
Subject: Re: [TN] BTC rework, Square SJs
Joyce,
You sound confusing. What do you mean by saying: "... Pb-rich and eutectic solder" in one sentence?
Regards,
Vladimir
Vladimir
SENTEC Testing Laboratory Inc.
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca
-----Original Message-----
From: Joyce Koo <[log in to unmask]>
Date: Mon, 1 Mar 2010 23:09:45
To: <[log in to unmask]>
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]]
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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