Hi Cedric,
Your last remark about standoff heights makes me feel curious. Do you mean
the higher the component is above the PCB, the better reliability? Is it
because elasticity of the assembly is increase?
No, it is not 'elasticity'—nothing elastic about solders, they creep.
For the same thermal expansion mismatch displacement, the strain in the SJs changes inversely with SJ height which in turn has a roughly power-of-2 relationship with cycles-to-failure.
Werner
-----Original Message-----
From: Cedric ORAIN <[log in to unmask]>
To: 'Werner Engelmaier' <[log in to unmask]>; [log in to unmask]
Sent: Wed, Apr 21, 2010 3:51 pm
Subject: RE: [TN] Head in Pillow and grapping effects mitigation without Nitrogen
Werner,
Solder grapping is a lack of coalescence of the solder paste that occurs on
low volume of paste. Whereas the solder joint is made between PCB and
component terminal, primary balls remains at the surface of the joint due to
oxidation. The root cause is the change in oxidation behaviour at very low
volumes of deposited paste :
- fine pitch => finer powder => higher surface area per volume => thicker
oxide layer
- Lower volume => higher oxidation, lower flux quantity
- …
(Read more:
http://www.indium.com/techlibrary/whitepapers/the-graping-phenomenon-improvi
ng-pbfree-solder-coalescence-through-process-and-material-optimization#ixzz0
llUIQVi6)
We encountered the head-on-pillow effect at the BGA periphery, furthermore
the design of the boards so that the center of the BGA is very unlikely the
colder area of the board. It should be a solderablity issue.
Your last remark about standoff heights makes me feel curious. Do you mean
the higher the component is above the PCB, the better reliability? Is it
because elasticity od the assembly is increase?
Cedric
________________________________________
De : Werner Engelmaier [mailto:[log in to unmask]]
Envoyé : mercredi 21 avril 2010 21:05
À : [log in to unmask]; [log in to unmask]
Objet : Re: [TN] Head in Pillow and grapping effects mitigation without
Nitrogen
Hi Cedric,
What do you mean by 'grapping effect"?
You do not say where you find 'Head-on-Pillow' defects—they can occur at the
BGA periphery and in the BGA center and the root cause is quite different.
HOP at the periphery is a solderability issue and certainly involves the
choice of paste/flux.
HOP in the BGA center means you do not have enough heat there to get the
solder ball to a low-viscosity liquid state—that means you need to increase
the peak reflow temperature.
One of the reasons for larger solder volumes is to achieve greater SJ
stand-off heights to improve reliability.
Werner
-----Original Message-----
From: Cedric ORAIN <[log in to unmask]>
To: [log in to unmask]
Sent: Wed, Apr 21, 2010 2:38 pm
Subject: [TN] Head in Pillow and grapping effects mitigation without
Nitrogen
Hello all,
Very fine pitch BGAs (typically 0.5mm) and 0201 chips are becoming common in
our company for some months.
We recently have to face with new defects type such as grapping effect and
head in pillow defect.
The solder paste we use has been qualified for even smaller component (WLP,
0.4mm pitch) but in Nitrogen atmosphere.
I'm now wondering if this solder paste is suitable with Air reflow. I'm also
wondering if a solder paste suitable in that case even exists.
Having a look to this study from intel (link hereunder, page 31), I found
that the people from Intel are recommending a solder paste volume larger
than 2000 mil^3 as a minimum.
http://edc.intel.com/Download.aspx?id=3044&returnurl=/default.aspx
That is, off-course, impossible for a VFBGA (which solder paste deposit is
closer to 900mil^3) but this reading makes me feel uncomfortable.
So the question is: is it possible to find out a solder paste which is
suitable for VFBGA assembly in Air reflow?
If it is not against TechNet rules, have you some solder paste references
that you could advise?
Here are some additional details: ENIG PCB finition, SAC305 Alloy.
Cedric ORAIN
Technical Director
Electronic Manufacturing Services
www.inovelec-groupe.com
PS: I'm very new and I'm also French. I wish it will not be too much for
you! Anyway, thank for being patient if I have difficulties to understand.
______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
for
additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
-----------------------------------------------------
______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
|
