target for good result with quality solder joint. Fine is not good enough. Agreed those mentioned form part of the process controls. With placement force, it will bring one to another level of process/assembly control. QFN is only a smaller issue when compared to LGA during SMT assembly.
________________________________
From: TechNet on behalf of Guy Ramsey
Sent: Thu 10/13/2011 11:40 PM
To: [log in to unmask]
Subject: Re: [TN] [DC] QFN layout
The QFN package provides only one important interconnect material; the
terminal. It, and the board must be solderable.
Design of the land pattern
Design of the stencil pattern
Selection and control of the solder paste
These provide the material component of the interconnect, they are critical.
If you have no control over these, you are at the mercy of these who do.
Solder performance of the package
Solder performance of the boards
Performance of the reflow oven (given oven settings to achieve an
appropriate time temperature profile).
In my experience placement is not a big problem.
Guy
From: Robert Kondner [mailto:[log in to unmask]]
Sent: Thursday, October 13, 2011 9:58 AM
To: 'TechNet E-Mail Forum'; 'Guy Ramsey'
Subject: RE: [TN] [DC] QFN layout
Guy,
We have 3 MY9s and a MY15. QFN placement is something that must be
constantly monitored. Not perfect but good machine. Anyone who say anything
more about a pick and place machine is a fool, liar or both. We get PCBs
from customers and we have zero chance to control land pattern designs.
It is not a QFN Placement problem we have here is a "Salesman Occupational
Hazard" we are dealing with.
Example:
Go into a Ford Dealership and ask a salesman if Fords are reliable cars.
You get: "Absolutely, No Problems!"
Go into a Toyota Dealership and ask a salesman if Toyotas are reliable
cars. You get: "Absolutely, No Problems!"
Go into a GM Dealership and ask a salesman if GMs are reliable cars. You
get: "Absolutely, No Problems!".
So when you go into an assembly house and ask if QFNs are easy to place and
you get " Absolutely, No Problems" guess what kind of person you are
talking to? Answer, a salesman.
Nothing wrong with sales folks but they are susceptible to a specific
occupational hazards. As sales folks are constantly dealing with "Smoke and
Mirrors" (just part of the trade) they tend to lose sight of truth. Placing
"Spin" truth is just part of their game.
Bob K.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
Sent: Thursday, October 13, 2011 8:18 AM
To: [log in to unmask]
Subject: Re: [TN] [DC] QFN layout
We have an MY15. We do a lot of QFN placement. We achieve fine results.
-----Original Message-----
From: TechNet <mailto:[mailto:[log in to unmask]]> [mailto:[log in to unmask]] On
Behalf Of Paul Edwards
Sent: Tuesday, October 11, 2011 12:46 PM
To: <mailto:[log in to unmask]> [log in to unmask]
Subject: Re: [TN] [DC] QFN layout
Bob,
We measure the part and PCB warp and vary the part vacuum release point
based on that to insure we are not deforming the printed solder paste
structure more than about 30%...
Because the MyData can't do that we don't typically use the MyData for
QFNs...
Paul
Paul Edwards
Process/Quality Engineering
Surface Art Engineering
-----Original Message-----
From: Robert Kondner <mailto:[mailto:[log in to unmask]]>
[mailto:[log in to unmask]]
Sent: Tuesday, October 11, 2011 9:49 AM
To: 'TechNet E-Mail Forum'; Paul Edwards
Subject: RE: [TN] [DC] QFN layout
Paul,
I don't think we are on the same wavelength.
Are you telling me you can drop a part 50mil onto a board to avoid pressing
it down into the paste? I cannot imagine doing that and getting any
placement accuracy. That would be nonsense.
It is in the force sensor where the machine detects board contact. Also,
watch the board deflection as a part is placed, you would be surprised. The
MyData's allowed me to slow down placement to where you can actually see
this deflection.
Bob K.
-----Original Message-----
From: TechNet <mailto:[mailto:[log in to unmask]]> [mailto:[log in to unmask]] On
Behalf Of Paul Edwards
Sent: Tuesday, October 11, 2011 12:09 PM
To: <mailto:[log in to unmask]> [log in to unmask]
Subject: Re: [TN] [DC] QFN layout
Normally we set the machines to a height placement point for QFNs to fix the
problem BUT you can do that on all machines and in ALL cases but when you
can it eliminates most of the problems...
Paul
Paul Edwards
Process/Quality Engineering
Surface Art Engineering
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