Guy,
I respectfully agree with your disagreement (can you do that?)... My point
was that our default parameters have changed with the new Pb-free solders.
Sometimes we have to adjust by looking at what we commonly call "best
practices" and re-visit the reason behind them, given the new set of
variables we have now. This may call for some thinking "out of the box", up
to and including what we have deemed "verboten" in the past. Pre-heating the
boards in question is an answer to this problem - possibly not the only
answer to it anymore, given the new world we find ourselves in.
Thanks for respectfully disagreeing. That's what this forum is all about...
Dale Ritzen
Quality Manager
Austin Manufacturing Services
-----Original Message-----
From: Guy Ramsey [mailto:[log in to unmask]]
Sent: Tuesday, October 09, 2007 2:46 PM
To: 'TechNet E-Mail Forum'; 'Dale Ritzen'
Subject: RE: [TN] RoHS solder and wetting plus thermal reliefs
I respectfully disagree, unless you can show that there aren't actually two
fillets one on the top and one on the bottom with a void in the middle.
In that case Phil would still have a fuse in the PTH where the copper is
thinnest.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dale Ritzen
Sent: Tuesday, October 09, 2007 3:45 PM
To: [log in to unmask]
Subject: Re: [TN] RoHS solder and wetting plus thermal reliefs
Hi Phil,
Quite possibly the industry norm for this type of situation has now changed
with the advent of RoHS compliant solders and their particular
idiosyncrasies. You may be right on the leading edge of those that define a
new norm to address this fill situation. Top-filling the solder junction may
indeed be the preferred method for handling this. We've all gotten used to
many "can't do's" over the years with leaded solders. We may have to
re-visit some of them, even against our better judgment, based on the new
solder types.
My 2 cents worth,
Dale Ritzen
Quality Manager
Austin Manufacturing Services
-----Original Message-----
From: Phil Nutting [mailto:[log in to unmask]]
Sent: Tuesday, October 09, 2007 2:10 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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