Jowan,
I think you are selling the heat gun short. I have used a Weller 6966 gun
for years. It is a small gun and is not like the "Paint Strippers" you
mentioned.
A lot comes down to the experience of an operator. A nice rework system
helps any day of the week but it is not required all the time. I have seen
folks mess up with rework stations.
Bob Kondner
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Iven, Jowan
Sent: Wednesday, October 21, 2009 9:09 AM
To: [log in to unmask]
Subject: Re: [TN] PWB Layout spacing queries
Hi Prashant,
The "alternative" repair method is not reliable.
First - the airgun.
You will never know which temperatures hit the board and adjacent
components.
Secondly- The connection for a QFN is made under the component, not at the
side. Although it migth work electrically at first, this is not a reliable
bond over time.
Not only the assembly process should be "in control" , also the repair
process. This often overlooked.
You need a decent repair station to achieve this.
Get rid of the hot air gun!
Or use it at home for a paint job.
Jowan Iven
Process Engineer
Neways Advanced Applications B.V.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of prashant chopra
Sent: Wednesday, October 21, 2009 2:43 PM
To: [log in to unmask]
Subject: PWB Layout spacing queries
Hi,
I have a couple of queries with regard to the component spacing ---
1. What should be the minimum spacing between the QFP and the nearest chip
components? (Assuming that the in case of failures the QFP will be reworked
manually using the soldering iron).
2. What should be the minimum spacing between the QFN package and the
nearest chip component? ( I am attaching a datasheet of QFN above).
3. What should be the minimum spacing between the 0402 component and the
other nearest 0402 component or chip component?
Also, I have one query reagrding the QFN rework process (datasheet attached
above) --
1. Ideally, in case of replacing the old QFN, the rework procedure should be
similar to the BGA rework procees and using the rework station and nozzle.
But, one of our manufactuirng location is not having the rework station.
They rework it manually, using the hot air gun to remove the component. Then
they place the new QFN component and solder the small portion visible on the
side edges (as shown in side view in data sheet) using the soldering iron.
But I believe, this will not allow much solder to flow below the part and
form contact there as major portion of the pad is below the body of the QFN.
Is this process reliable? Will it have any impact on the performance over a
period of time? is there any other reliable manual process which can be used
for this rework?
Appreciate all your help and response. Thanks in advance.
Rgds
Prashant
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