You should be able to use the land pattern calculator, either using the 3
formulae in IPC-SM-782 or from IPC's on-line calculator, as the result is
entirely based on the dimensions for max overall length, lead with, lead
contact length, with an RMS value for component tolerence (Ct), PCB
manufacturing tolerence (Mt) and P&P machine placement tolerence (Pt) i.e.
sq.rt.(Ct^2 + Mt^2 + Pt^2).
Otherwise, I suggest a rough calculation of max lead width + 0.02mm either
side for side fillet, max lead contact length + 0.4mm onto the outside and
0.3mm onto the inside for toe and heel fillets. For larger components, you
can almost discount the tolerences of manufacturing and placement
tolerences, as they're relatively quite small compared with component
tolerence, but for this device, if you have room between pads, I'ld at
least see what the RMS tolerence value does to the pad width and make a
judgement based on experience from there. Ball back in your court a bit.
I asked Technet for its opinion on calculating non-standard land patterns a
couple of weeks ago, and the answer from IPC was that they were working on
these issues, so really, you guess is as good as anyone else's.
Peter Duncan
"Braime,
Justin" To: [log in to unmask]
<jbraime@RACALI cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST
NST.CO.UK> Aero/ST Group)
Sent by: Subject: [TN] LCC 20-pin 4x4mm
TechNet
<[log in to unmask]
G>
10/12/01 03:33
PM
Please respond
to "TechNet
E-Mail Forum."
Hi guys,
Anybody come across an LCC with 20 pins and only 4mm square? I'm looking at
one from RF MicroDevices - and their datasheet is lacking in the land
pattern department (very helpful...)
I need some advice re: land pattern design. IPC land pattern calc is no use
- it's not a standard LCC design.
All help gratefully received :)
Thanks
Justin Braime
Senior Production Engineer
Thales Instruments Ltd
480 Bath Rd, Slough
Berkshire, SL1 6BE
England
Tel: +44 (0)1628 604455
Fax: +44 (0)1628 662017
E-mail: [log in to unmask]
**********************************************************************
This email and any files transmitted with it are confidential and
intended solely for the use of the individual or entity to whom they
are addressed. If you have received this email in error please notify
the system manager.
This footnote also confirms that this email message has been swept by
MIMEsweeper for the presence of computer viruses.
www.mimesweeper.com
**********************************************************************
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
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 delivery of Technet send the following message: SET
Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases >
E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
---------------------------------------------------------------------------------
[This e-mail is confidential and may also be privileged. If you are not the
intended recipient, please delete it and notify us immediately; you should
not copy or use it for any purpose, nor disclose its contents to any other
person. Thank you.]
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
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 delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------
|
