TECHNET Archives

July 2014

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Graham Collins <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Graham Collins <[log in to unmask]>
Date:
Fri, 25 Jul 2014 08:18:20 -0300
Content-Type:
text/plain
Parts/Attachments:
text/plain (65 lines)
Hi Stephen
Two quick tests
  - run it with Nitrogen off (assuming you are reflowing in Nitrogen)
  - rotate the board 90 degrees on the conveyor

After that I'd look at the stencil, cut the amount of paste down. Given 
your comment about qualification I'm guessing that changing the paste 
would involve jumping through a lot of hoops...

I had a board once, same deal - 0603 parts tombstoning like crazy, pads 
were too big and no way was that going to get fixed.  We started running 
it in air for reflow, problem went away.

regards,

Graham Collins
Senior Process Engineer
Sunsel Systems
(902) 444-7867 ext 211

On 7/24/2014 4:57 PM, Vargas, Stephen M wrote:
> Hello All:
>
> We are experiencing a high rate of tombstoning on two particular package styles (0508 and 0612 capacitors) on an assembly here. The rest of the board solders at a normal defect rate. Here are some of the things we have looked at and some aspects of our process:
>
> I've tried using two different profiles (straight ramp to peak and a ramp, soak, spike).
> I've moved the parts from our high speed chip shooter to our flexible placement machine to optimize placement accuracy.
> The pad layout (which is not an option for change due to the product having already been qualified by our customer) is very close to the manufacturer's recommended layout and the board finish is immersion silver.
> We are printing 1:1, no aperture micro-modifications.
> Stencil thickness is 6 mils. I'm concerned about moving to a thicker stencil due to having 20 mil pitch parts on the board.
> Our paste is a low residue / pin probe-able no-clean 63/37 (again not an option for change).
> We also looked at which side of the device is connected to ground, assuming that this side of the device would heat up more slowly causing a tombstoning condition pivoting at the non-ground side. But there was no trend indicating that this was the case.
> Solder mask height measured in between the two pads and it was determined to be at the same height as the pads
>
> I've attached a link to the datasheet for one of the devices for reference. I'm wondering if the forces of physics make this part more susceptible to tombstoning due to the terminations being on the long side of the device. Any ideas on how we can improve our yields? Thanks.
>
> http://www.avx.com/docs/Catalogs/licc.pdf
>
> Regards,
> Steve Vargas
>
> If you don't have time to do it right, when will you have time to do it over?
> John Wooden
>
> Polaris Contract Mfg Inc
> 15 Barnabas Rd
> Marion, MA 02738
> 774-553-6192
> [log in to unmask]<mailto:[log in to unmask]>
>
> P Please consider the environment before printing this e-mail
>
>
> ______________________________________________________________________
> This email has been scanned by the Symantec Email Security.cloud service.
> For more information please contact helpdesk at x2960 or [log in to unmask]
> ______________________________________________________________________
>


______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________

ATOM RSS1 RSS2