I would agree.
From the description this is a fast process, the solder wicks straight up the pin (one interpretation of this is that 'straight' means 'immediately'), copper dissolution takes time and wetting to a normal barrel would be apparent and then degenerate as the barrel disappears. If the barrel were very thin then it could disappear quickly. Have you done as recommended and checked your barrels?
We have done experiments to measure dissolution in our wave. It is significant and cannot be ignored. Rework cycles make this much worse.
Regards
Rex
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Neifer, Gebhard
Sent: 28 July 2011 07:43
To: [log in to unmask]
Subject: [TN] AW: [TN] Missing PTH Barrels in Connector
As the amount of tin in a reflow and in a hand solder process is limited, to me it looks like copper dissolution is probably not the main cause of your issue...
Gebhard
-----Ursprüngliche Nachricht-----
Von: TechNet [mailto:[log in to unmask]] Im Auftrag von Joyce Koo
Gesendet: Donnerstag, 28. Juli 2011 04:23
An: [log in to unmask]
Betreff: Re: [TN] Missing PTH Barrels in Connector
What is the barrel thickness? Did you etch it and see how is the seed layer and subsequent 1st layer adhesion the the PWB? Any etchback can be observed? You do not need to answer my question. As long as you find out the answer.
--------------------------
Sent using BlackBerry
----- Original Message -----
From: Thomas Bauer [mailto:[log in to unmask]]
Sent: Wednesday, July 27, 2011 10:07 PM
To: [log in to unmask] <[log in to unmask]>
Subject: Re: [TN] Missing PTH Barrels in Connector
Hello
Do you know if there are inner layer pads helping secure the structural integrity of the pth? If not I could see how overheating during soldering could easily cause the barrel to pull out of the hole.
Thomas
On Jul 27, 2011, at 5:42 PM, "Tom Burek" <[log in to unmask]> wrote:
> Hello,
> I have a PCA that hand solders 6 connector pins to an 4 layer PCB
> assembly.
> The finish on the PCB is Lead Free HASL (SN100CL) and the solder used
> to hand solder the pins is SAC305. The hand soldering is performed as
> a secondary assembly operation after reflow.
> What happens to some of the assemblies, but not all of them, is that
> the solder will wick straight up the pin, thereby not allowing a Solder joint.
> The pin can be pulled right out of the hole, revealing a PTH with no
> inner barrel.
> Completely wiped out as if it was never there in the first place.
> This phenomenon is not present on every PCB or every pin of the same connector.
> The PCB's are part of a multi-board panel.
>
> As far as I know the PCB started out with a barrel, but I cannot rely
> on this being the case as I do not believe the technician checks 100%
> of the PTH's prior to inserting the pin.
>
> Am I looking at excessive heat causing complete Copper Dissolution of
> the PTH barrel?
> or
> A PCB that may not have a barrel in every hole, part of the PCB
> fabrication process?
> or
> Any other suggestion as to which direction to head would be appreciated.
>
> Thanks in advance.
>
>
> Tom Burek, CID+
>
>
>
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