Matt,
We've found IPC-SM-782A to be excellent for IR and Vapor-phase
reflow
assembly, based on feed-back from our assembly sub-contractors. I can't
speak for
wave soldering, however.
As far as what it covers, that's kind of an interesting question. I
doesn't
attempt to be the definitive land pattern standard for every package ever
manufactured
anywhere by anyone.
What it does cover are a number of standardized package "types".
This
includes most of the ceramic SMT resistors and capacitors, soics, ssoics,
plccs,
qfps, sqfps, "to" styles, melfs, etc. More importantly, it provides tables
of values
for lead span, lead width and other dimensions along with the recommended
land
pattern. You can often interpolate from the tables for land patterns not
shown.
Finally, formulas are given for how the land patterns were derived
for
various lead types; gull-wing, j-style, metalized end-caps, and so on. There
are
Windows/95 compatible spread sheets available from IPC for automating the
calculations.
We also in the past have used the part manufacturers recommended
land patterns with decidedly mixed results. We've since stopped, and now
calculate
all of our land patterns from IPC-SM-782A.
Michael Hiteshew
Lockheed Martin Launching Systems
[log in to unmask]
(410) 682-1259
> ----------
> From: Matthew
> Lamkin[SMTP:[log in to unmask]]
> Reply To: TechNet E-Mail Forum.;Matthew Lamkin
> Sent: Thursday, January 21, 1999 3:07 AM
> To: [log in to unmask]
> Subject: [TN] SMT land pattern standards?
>
> Hi there all you IPC guys, can someone help me to determine what the
> best collection
> of standard SMT land pattern designs is?
>
> I use convection reflow on a QUAD machine for the majority and will
> shortly be using wave solder on a BLUNDELL machine.
>
> We are having a few problems that are being claimed as wrong footprint
> sizes, and to be honest this could be true as
> the footprints were not entered into our CADSTAR cad system in-house.
>
> There seems to be little published material available in the U.K. as
> complete documents to specify
> sizes for the most commonly used devices & I was wondering if anyone
> could tell me what the IPC-SM-782A
> document is like ?
>
> I.E. how many components does it cover & how much detail does it give
> for each one ? Does it give clear differences
> between each soldering method & how good are these footprint
> sizes?
>
> Any footprints that have been designed in-house have come from differing
> manufacturers data books that could
> be out of date or the component could come from differing manufacturers.
>
> Any help is appreciated.
>
> T.T.F.N
>
> Matthew Lamkin
> Printed Circuit Board Draughtsman
> Protec Fire Detection PLC
> Churchill Way,
> Nelson, Lancs
> BB9 6RT.
> Tel 01282 717393
> Fax 01282 717273
> Email = [log in to unmask]
>
>
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