TECHNET Archives

July 2010

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:
vladimir Igoshev <[log in to unmask]>
Reply To:
Date:
Tue, 6 Jul 2010 11:51:11 +0000
Content-Type:
text/plain
Parts/Attachments:
text/plain (1 lines)
Ashok,

from my experience (including automotive assemblies) QFNs are always slightly tilted. However, having a specified minimal thickness of solder has never been of concern to our customers.
Vladimir

SENTEC Testing Laboratory Inc.
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca

-----Original Message-----
From: Ashok Dhawan <[log in to unmask]>
Sender: TechNet <[log in to unmask]>
Date:         Mon, 5 Jul 2010 22:50:08 
To: <[log in to unmask]>
Reply-To: TechNet E-Mail Forum <[log in to unmask]>,
        Ashok Dhawan <[log in to unmask]>
Subject: Re: [TN] QFN : what is minimum solder thickness to rework

Werner

I am having limited info and am looking from experts on technet to provide
guidance using limited info when to rework and when to let go.

If device is tilted, the thickness will be different from one end to other
end. what basis to use for rework for tilt ? My own guess is it can be based
on minimum thickness, if it was within acceptable range of thickness, tilt
will be acceptable.

I am urging all technet experts to share their experience on this subject.   


Answers to questions are listed below :  

The minimum solder joint thickness depends on 5 parameters:
(1) the size of the QFN,------ QFN-32 is 2 mm x 2 mm Package with 10x 19 mil
signal pins and 120 x 120 mils cooling plate.
(2) the CTE-mismatch with the PCB,-----Do not know. It is plastic
package,board is FR4 , soldered with Tin-lead solder.Peak treflow is 225-230
deg C.

(3) the delta-T, -----the operating temperature range for the product is -55
deg C to 125 deg C. I do not know junction temperature range.
  
(4) the reliability requirement in terms of number of cycles, and

---- Do not know. The expected life of product is 5 to 10 years.

(5) the reliability requirement in terms of acceptable failure probability.
------ Do not know.

How all of this hangs together, can be found in IPC-D-279; alternatively,
you can take my workshop on fundamentals of solder joint reliability.

---------- Please provide me info if there is an upcoming webtorial on this.



 Regards

Ashok Dhawan, P. Eng. 
Manufacturing Specialist 
Parker Hannifin Electronic Controls
Electronic Controls Division
1305 Clarence Avenue
Winnipeg, MB  R3T 1T4 Canada
direct 204 453 3339 x390 
fax 204 452 6801 
[log in to unmask]
www.parker.com/ecd

---------------------------------------------------
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] 
______________________________________________________________________

ATOM RSS1 RSS2