Hi John,
You have to find out what are the causes of failures. It seems to me that there are open and short problems from you email.
Short is "easier" to eliminate if it is not related to design problem. Change the pads deign to 16mils for 13mm X 13mm or reduce the aperture opening on this chip. I believed that short issue only related to this 13mm X 13mm BGAs.
Open is much more difficult to handle, there are lots of processes that can caused the opened issue. Does the opening only occur at some BGAs points? You might want to do a dye and pry on the 13mm X 13mm BGAs to determine the open is at the BGA substance or at PCB pad side?
Does the 37.5mmx37.5mm BGAs subject to thermal stress during wave soldering process (if there is this process)? You might want to increase the pads design to 26mils-29mils.
Do go for 50 to 60sec for TAL time.
Others seem good!
Regards
GA Tan
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Queen
Sent: Sunday, 17 August 2008 2:05 PM
To: [log in to unmask]
Subject: Re: [TN] BGA reballing
Some more details thanks for the input
1. BGA component information.
A) Component Type Plastic BGA
B) Ball pitch is 50 mil,31.5 mil
C) Ball diameter,24 mil,12.0 mil
D) Solder Ball alloy composition Leaded Sn/Tn----- 63/37
E) Ball count 841,144
F) Package Size,U14 37.5 mmX 37.5 mm,13mm X 13mm
2. PCB fabrication,
A) PCB finish, HASL Finish
B) Pad size, 24 mil,,12.5 mil
C) Pad shape, circular
D) Pad design is SMDP
3. Stencil fabrication methodology. (Laser cut or E-Fab),Stencil is
laser cut with electro polishing
B) Aperture size,24 mil,16 mil
D) Aperture shape, Circular
E) Solder volume, We measure solders paste height . Average paste
height 5 mil
4. Oven Profile
A) Ramp-up, 0 to 3 degree/sec
B) Soak time, 60 to 90 sec
C) Soak Temp.130 to 160 degree C
D) Peak temp,210 to 230 degree C
E) TAL time,30 to 90 sec
F) Cool Down.0 t0 3 degree/sec
G) Soft copy of reflow profile. Please refer the attached file for
reflow profile as well as for BGA data sheet.
5. X-Ray images,Please refer the attached file for X ray images.
John
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /*
Sent: 16 August 2008 19:43
To: [log in to unmask]
Subject: Re: [TN] BGA reballing
Hi john,
You are skimpy on the details.
What solder prior and after reballing? What cause the failure? Failure mode?
Mechanism?
Whats causing the shorts? Where?
Werner
Future workshops:
Reliability Issues with Lead-Free Soldering Processes, September 22,
Schaumburg
Failure Mode and Root Cause Analyses Reliability (Fatigue, Brittle Fracture,
ENIG), September 22, Schaumburg
Solder Joint Reliability: Parts 1 & 4, Oct. 9, Moscow, Russia
Solder Joint Reliability: Part 4, Oct. 17, Timisoara, Rumania
Solder Joint Reliability: Parts 1 & 4, Oct. 22, Tallinn, Estonia
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