Hi,
If there is board space within a 2 or 3 inch radius and you have planes for
these voltages (I assume they are on planes) the mounting caps one on top of
each other is not required.
Even in a BGA you have little itty bitty bonding wires with more inductance
that a couple inches of plane. Take you highest power frequency and compute
the wavelength. Then take that frequency and calculate the inductance of 3mm
of trace length. Using the wavelength / 10 of the board, plane impedance and
the Z of the caps you will find stacking just does not buy anything.
Bob Kondner
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
Sent: Wednesday, March 03, 2010 11:43 AM
To: [log in to unmask]
Subject: Re: [TN] Unusual Assembly Requirement...
We did the board in two reflow cycles.
Print, place, dispense, place reflow.
Dispense, place, dispense place reflow.
A three high stack is more common, one reflow.
Just make sure the convection fans are on low, and the parts are very
solderable to start.
A tombstone or drawbridge ruins your whole day.
Though the speed is a few Ghz the devise on the opposite side of the board
is digital.
Remember when we used to think a 10Mhz clock was really fast?
I had a DELL 286 with 8 to 12.5 Mhz clock that, according to PC Mag, was
fast enough to burn sand off the desert floor.
Guy
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez
Sent: Wednesday, March 03, 2010 6:09 AM
To: [log in to unmask]
Subject: Re: [TN] Unusual Assembly Requirement...
What was the total number of reflows?
Vic,
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Tuesday, March 02, 2010 2:39 PM
To: [log in to unmask]
Subject: Re: [TN] Unusual Assembly Requirement...
Hi Jon,
Yes these are individual caps, each layer is a different value. The board
was screen printed and the bottom layer was machine placed. The next layer
was done by hand dispensing solder paste on each cap termination, and then
hand placing the second layer caps. The board was then reflowed. After
reflow, paste was again hand dispensed on the second layer caps
terminations, the third layer caps were hand placed, and then solder paste
was hand dispensed on the third layer caps termination. Finally the fourth
layer caps were hand placed, and the board sent back through reflow the
second time.
We needed to do it in two reflow steps otherwise the stacks would have
toppled over into each other...
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Roberts, Jon (SA-1)
Sent: Tuesday, March 02, 2010 3:04 PM
To: [log in to unmask]
Subject: Re: [TN] Unusual Assembly Requirement...
Steve, these were all individual caps? We have used double stack caps that
were manufactured that way. It just looks fragile. Jon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Tuesday, March 02, 2010 1:52 PM
To: [log in to unmask]
Subject: [TN] Unusual Assembly Requirement...
Hi All,
I came into work today and saw something that I've not seen before. Keep in
mind that the area shown is about ½" square, and that these are 0402's...
http://stevezeva.homestead.com/files/Quad_Stack.JPG
This was done using two reflows, and the caps were not touched by a
soldering iron.
You may ask why. It's because it's what we were asked to do by our customer.
We have a very talented lady working on the production floor who
accomplished this.
Steve
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