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October 2011

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Subject:
From:
Steve Gregory <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Steve Gregory <[log in to unmask]>
Date:
Fri, 14 Oct 2011 12:15:56 -0400
Content-Type:
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text/plain (179 lines)
Hi Bob,

If you knew Guy, you would know that he is not a salesman... :^) neither am
I.

But he is right, we do place a lot of QFN's with our MY15 ECR and don't have
many problems with them. Here's an example. It's a 93K ATE board that's 17"
X 23" and this particular board has about 60-70 QFN's on it, a mix of
2-sided and 4-sided QFN's:

http://stevezeva.homestead.com/93K_Board.JPG

http://stevezeva.homestead.com/LottoQFN.JPG

We do boards with more than that, and some with less. I won't say that we
don't ever have problems, because we occasionally do just like everybody
else. But IMHO our MY15 does a pretty good job.

BTW, we don't have to worry about board deflection on boards like in my
picture, it's .230" thick and doesn't deflect much. But even if it did,
isn't that what board supports are for?

Steve 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Thursday, October 13, 2011 9:58 AM
To: [log in to unmask]
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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