I do not normally plug a product but just something I wanted to pass on
to all of you. I recently evaluated a number of wave solder fluxes for a
Pb-free wave solder process for one of my own clients (not GD) where it
was critical that 100% hole fill was achieved on some backplane
connectors that saw mating/unmating forces several times during its
life. There was a single flux that stood out in terms of promoting
topside fillets on these massive connectors that were otherwise very
difficult to solder. Out of 5 different fluxes tested, this was the only
one that ensured 100% hole fill and 100% fillet formation on the top
side of the board (under the connector). That flux was Qualitek 775A.
http://www.qualitek.com/775_TDS.pdf
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Nutting
Sent: Wednesday, October 10, 2007 7:38 AM
To: [log in to unmask]
Subject: Re: [TN] RoHS solder and wetting plus thermal reliefs
Paymon,
What aggressive fluxes are you using?
Phil
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paymon Sani
Sent: Tuesday, October 09, 2007 4:51 PM
To: [log in to unmask]
Subject: Re: [TN] RoHS solder and wetting plus thermal reliefs
Hello Phil,
Guy is correct. You need to preheat the boards and use aggressive
fluxes. We use the SnC100 with our wave soldering process and we get
100% barrel fill even-though we only need to meet the IPC specification!
Paymon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
Sent: October 9, 2007 3:46 PM
To: [log in to unmask]
Subject: Re: [TN] RoHS solder and wetting plus thermal reliefs
We are doing 100% vertical fill on 5 mm thick 32 layer boards with
multiple ground planes, Pb-Free solder. It requires preheat.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Nutting
Sent: Tuesday, October 09, 2007 3:10 PM
To: [log in to unmask]
Subject: [TN] RoHS solder and wetting plus thermal reliefs
Hello Technetters,
Let me see if I can explain the problem. We build some PTH boards with
4 oz. copper and connect some high power IGBT devices with thermal
reliefs on the pads. In the past with tin/lead everything worked well.
More of our designs are being converted over to RoHS (SAC 305). It
appears we are not getting as much flow through or wetting on these
devices. So there is a two fold concern. During a specific failure
mode the thermal reliefs act like a fuse causing arcing until enough
copper vaporizes to make a large enough gap that the voltage can no
longer jump. One solution is remove the thermal reliefs. Part two is
the amount of current passing through the PTH. We can't rely on the
barrel for full current carrying capacity so 100% barrel fill is desired
with a good fillet top and bottom.
Here is where we are having issues with RoHS solder not fully wetting or
filling the PTH.
I'm concerned that removing the thermal reliefs will generate other
problems. I'm thinking we should use a different configuration relief.
If the RoHS solder does not fill the hole we would typically go back and
top solder the connection. I know the industry considers this a no-no.
Any recommendations?
Thanks in advance.
Phil Nutting
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