Bev,
I saw it without drops and not in the corner, but inside balls. It depends on how the package warps.
Vladimir
SENTEC
SENTEC
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca
-----Original Message-----
From: Bev Christian <[log in to unmask]>
Date: Thu, 11 Jun 2009 18:18:46
To: <[log in to unmask]>
Subject: Re: [TN] Corner ball pad cratering
Wow. Never saw it except after multiple drops.
Bev
RIM
----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Thu Jun 11 18:15:46 2009
Subject: Re: [TN] Corner ball pad cratering
That may be the case sometimes that pad cratering will occur just from the reflow process. We have some reason to suspect that it could occur later, due to some unique mounting of mechanical components, the size of the PCB (the potential for deflection), and when the defect seems to show up in the test process.
Genny
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /*
Sent: June 11, 2009 3:33 PM
To: [log in to unmask]
Subject: Re: [TN] Corner ball pad cratering
Hi Genny,
Bythe time you can underfill, you already have pad cratering-so this does not help.
Why pad cratering?
Remember, 'pad cratering' results from a number of factors coming together. Those factors are: 1) SAC solders are about 40% stiffer generating higher forces on cooling; 2) SAC solders creep significantly slower and thus do not provide stress relief on cooling; 3) the delta-T between solder solidification and the glass transition temperature, Tg, doubles for SAC-solders thus doubling the thermal expansion mismatch and the resulting stresses; 4) for some PWB base materials the fillers and curing agents used to make the resin RoHS-compatible make the resin more brittle with less cohesive strength.
Solution Options: 1) reduce cooling rate from soldering to no more than 1.5°C/sec; 2) use PWB base materials with higher Tg; 3) increase solder joint thickness between component and soldering pad; and 4) my favorite, go back to environmentally friendly SnPb solder.
Werner
-----Original Message-----
From: Genny Gibbard <[log in to unmask]>
To: [log in to unmask]
Sent: Thu, 11 Jun 2009 4:09 pm
Subject: [TN] Corner ball pad cratering
Hello all,
If you have identified a BGA with corner ball pad cratering, what would be your suggestions to correct this condition?
Our thoughts:
1. We plan to evaluate our handling processes to reduce/remove excessive flex/strain occurring around this part 2. We plan to evaluate corner bonding or underfilling for the BGA.
Which=2
0do you feel would be the best direction to go? Do you have other suggestions?
Thanks in advance for all your help
Genny
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