Since it is an old board, is it Pb-sn lead and soldered on lead free temp?
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----- Original Message -----
From: Thayer, Wayne - IIW [mailto:[log in to unmask]]
Sent: Tuesday, December 06, 2011 05:36 PM
To: [log in to unmask] <[log in to unmask]>
Subject: Re: [TN] NTC - Experimenting with new microscope camera
I think Richard's on the right track with the solder plated leads. That's all you need to make this happen: During reflow the molding compound puts pressure on molten solder on the lead, forcing the solder to "squirt" out onto the lead which has no flux on it, so the solder beads up on top of the oxides.
This phenomenon is the bane of flipchips: if the solder joints can find a void (such as may happen due to poor adhesion between underfill and the surface of the die or the surface of solder mask), then solder will "squirt" in causing shorts.
On your capacitor, it is probably no big deal except that you have an easier path for moisture to get in and do nasty things.
Wayne Thayer
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Tuesday, December 06, 2011 2:28 PM
To: [log in to unmask]
Subject: Re: [TN] NTC - Experimenting with new microscope camera
Not necessarily the supplier, at least not directly.
That type of solder beading, for lack of a better term, shows up like that during tinning/plating processes. The reason for it is due to residues from the encapsulation or molding on the lead near the body that prevent solder wetting. Those may be droplets of non-wetted solder from tinning, not necessarily solder squeeze-out from under the molded package. If it was solder from under the molded package, why did it not wet out onto the lead?
But no matter the source of the solder, it showed up as an issue due to poor solderability in the area where the lead enters the package body.
Also consider the leads may have been stamped from a sheet of metal that had been pre-coated with solder, in which case the squeeze-out could occur during reflow soldering later.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: Tuesday, December 06, 2011 11:48 AM
To: [log in to unmask]
Subject: Re: [TN] NTC - Experimenting with new microscope camera
I've seen this before as well on similar diode packages. I don't think we were ever able to discover the actual root cause, though the supplier would almost certainly be the culprit.
Leland
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick
Sent: Tuesday, December 06, 2011 12:20 PM
To: [log in to unmask]
Subject: [TN] NTC - Experimenting with new microscope camera
All,
I recently purchased a microscope camera and have been trying it out on various items.
Have placed two photos on the IPC website which I believe illustrate a tin [or solder plated] lead on which the plating has reflowed and squirted out from beneath the mold compound.
Have seen similar manifestations with improperly processed solder & glob-topped assemblies.
http://ipc-technet.groupsite.com/gallery/22093 filed alphabetically under folder name - Tin Plated Leads
Anyone else have other ideas?
Please keep in mind that this an old modem board of unknown chronological vintage that I had in my 'scrap bin'. It just happened to be the subject of my scrutiny.
I see no evidence of solder balls, etc on the board.
Steve
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