TECHNET Archives

March 2006

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:
Rodney Miller <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Rodney Miller <[log in to unmask]>
Date:
Thu, 30 Mar 2006 09:06:57 -0600
Content-Type:
text/plain
Parts/Attachments:
text/plain (199 lines)
I'm not sure your problem is related to solder tension "lifting up" and
causing the part to float.

Pending how you have the heat slug designed.  I think the "window
paning" is the way to go.  That's the same concept we use on
nonsymetrical packages like TO-223 etc, and we manage the paste
application to allow the part to selfcenter, which if tension was
"lifting" the application like yours wouldn't work.

Almost sounds liken and oven issue and irregular heating to me.  Solder
type and finish could be playing a part, I'm guessing you are ENIG, but
also the Z placement force and powder could be working against you.

In essence this part should self-align with a 5 or 6 mil stencil.  If
smaller, your CM should overcut the aperatures to allow the paste to be
adequate volume.

Lastly, if you really feel the parts heat slug is "fighting" the leads,
that's an easily proved theory.  Have the CM do a heat profile and
determine which is reflowing first, upon knowing this, you should be
more prepared to determine where the problem lies.  Dropping some Vias
into your HeatSink Pad or adjusting your stencil "Window Paning" should
allow you to manage movement on this part.  You might even change your
stencil aperature on the leads to a "C" shape to counter act their late
reflow if that is the case.

The pitch on the package surprises me that you are having that much
movement?  Is it Forced Air Convection oven?  Seems to me you might
review the Reflow heat profiles, they may tell you a different story.

IMHO

I did stay at a Holiday Inn last nite LOL

-----Original Message-----
From: Dave Seymour [mailto:[log in to unmask]]
Sent: Wednesday, March 29, 2006 9:11 AM
Subject: Re: SO8 with Heatslug


Steve,

I agree the manufacturer should be the primary source.

In the this particular case ( pun intended), It depends.

The Phillips site varies depending on package.

In the document listed, BGA Geometry :
http://www.semiconductors.philips.com/acrobat_download/various/Surface_m
ount_reflow_soldering.pdf

Recommends 20%-35%, as mentioned.


In another document, different package (DWFN):
http://www.standardics.philips.com/support/documents/logic/pdf/dqfn.sold
er.pdf

Recommends 80%

As far as the original question, with a So8 heat slug package,  I'm
waiting on Phillips to get back to me.

I talked to our Contract Assembly house to get their opinion. The CM's
opinion was closer to the 70-75% coverage.

The line of thinking is the same, reduce the volume of paste for heat
slug devices. The amount of reduction is package and process related.
Work with the assembler to refine the process for consistent results.

Thanks to all who responded.

Dave


Steve Mikell wrote:

>Dave,
>
>I always suggest reading the manufacturer's information. Philips should

>know how to use their own parts.
>
>Please visit ............
>http://www.semiconductors.philips.com/acrobat_download/various/Surface_
>mount_reflow_soldering.pdf
>
>On page 16 they discuss the recommendations for large pads and thermal
>attachment.
>
>The numbers are 20-35%, not 70%. remember, this may change by component

>manufacturer, so the other guys may be right about 70%, but for the
>components they are using.
>
>Good Luck
>
>Steve Mikell
>[log in to unmask]
>
>
>
>>----- Original Message -----
>>From: "Dave Seymour" <[log in to unmask]>
>>To: [log in to unmask]
>>Subject: [TN] SO8 with Heatslug
>>Date:         Tue, 28 Mar 2006 10:30:33 -0500
>>
>>
>>Currently using a Phillips part,
>>
>>http://www.semiconductors.philips.com/pip/NE57814DD.html
>>
>>This is a  standard SO8 package with a large "heat slug pad" under the

>>part.
>>
>>During reflow the part is floating off center and causing shorts to
>>the lead pads. I believe this because of the the volume of paste in
>>the heat slug area is lifting the
>>part up and surface tensions take over.
>>
>>I have a call into tech support at Phillips, but I figured I would
>>query while waiting for a call back.
>>
>>What is the recommended volume of solder paste under this device ?
>>
>>What is the recommended solder mask opening(s) under this device?
>>- Something like 4-6 smaller opening over a continuous top side ground

>>plane?
>>
>>What is the recommended paste printing pattern under this device?
>>- match the soldermask openings?
>>
>>Does anyone have experience with such a device?
>>
>>Thanks,
>>
>>Dave
>>
>>
>>--
>>Dave Seymour, CID+
>>Catapult Communications Inc.
>>800 Perimeter Park Dr, Suite A
>>Morrisville, NC 27560
>>
>>Direct: (919)653-4249
>>Main: (919)653-4180
>>Fax: (919)653-4297
>>
>>[log in to unmask]
>>
>>
>>
>
>
>
>

--
Dave Seymour, CID+
Catapult Communications Inc.
800 Perimeter Park Dr, Suite A
Morrisville, NC 27560

Direct: (919)653-4249
Main: (919)653-4180
Fax: (919)653-4297

[log in to unmask]



---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
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
-----------------------------------------------------

ATOM RSS1 RSS2