Hi Russell
Is it skewed before it goes into the reflow oven?  If yes, then a
placement issue.  If it looks OK before reflow oven and is skewed after
the reflow oven then obviously is moving in there - which points to a
pad size problem.

If their placement is good and it is skewing in the oven, one trick we
have used in the past is to dispense a glue dot under the component body
- it will hold the alignment during reflow.  We have used this method
when pad layout is not quite right and the alignment is critical to meet
IPC-A-610 requirements (e.g. for heel fillet).  They would need to have
glue dispense capability though.

regards,
 - Graham

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Nowland, Russell
Howard (Russell)
Sent: Monday, March 22, 2010 4:57 PM
To: [log in to unmask]
Subject: [TN] TI/Emerson SMT Board Mounted Power

Hello Technetters,

I have a problem I hope someone out there has a solution for.

I have on a PCA that uses a Texas Instrument/(Emerson Power/Artesyn)
(dual sourced but part of the POLA) SMT board mounted power converter.
The MPN is PTH03050WAS.  It is actually combination PTH and SMT.  The
device has 40 mil diameter pins for PTH and to make it SMT they simply
add a donut (solder dam) on the pin and round the edges and call it a
solder ball.  I think the problem my EMS is having is really with
pick-n-place because the pick-up point (Actually the top of a
transformer) is off-center, fairly small, and it has a plastic label on
it.

The problem is the device is coming out of the oven skewed and violating
IPC 610D.  The pad diameter is exactly what is recommended by the
datasheet (.085-inches).  The TI datasheet recommended a 0.080-0.085
diameter aperture @ six mils.  Originally my EMS had 0.085-inch @ 5 mils
but changed the aperture to a bull's-eye shape with the thought the
bull's-eye would help center the device.  Both of the stencils have
failed to draw the device to the center.

Because this is really a Butt Joint I am holding the EMS to no side
overhang.  This is causing them quite a headache. They have also not
come up with a viable solution either.

Here is the link to the data sheet

http://www.emerson.com/sites/network_power/en-US/Products/Product_Detail
/Product1/Documents/PTH03050%20DC-DC%20Converter/PTH03050%20Data%20Sheet
.pdf



Has anybody used these devices with good results?  If so can you share
your methodology?

Thanks in advanced,


Russell Nowland
Alcatel-Lucent
Advanced Manufacturing Engineer
Address: 14000 Quail Spring Parkway, Suite 300
Oklahoma City, OK 73134
email:
[log in to unmask]<mailto:russell.nowland@alcatel-lucent
.com>
Desk: 405-302-1660
Cell: 405-203-0034
Fax: 405-302-1622


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