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October 2002

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Subject:
From:
"d. terstegge" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 31 Oct 2002 15:31:52 +0100
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Hi Mike, 

Yes this was prior to assembly, it's not localised areas of bare copper
but several pads having a dull appearence and a color somewhere between
brown, green, and solder. There's no solder dome, it's very flat.

Daan Terstegge
Unclassified mail


>>> [log in to unmask] 10/31/02 02:23pm >>>
Was there Cu exposed on the bare PWB you inspected, prior to assembly
/
soldering? 

-----Original Message-----
From: d. terstegge [mailto:[log in to unmask]] 
Sent: Thursday, October 31, 2002 6:00 AM
To: [log in to unmask] 
Subject: [TN] HASL process OK or not ?


Hi Technet,

Yesterday I visited one of our bare board manufacturers and had a
close
look at their HASL-process. The reason for the visit was solderability
problems on BGA-pads, which sometimes look thin and dull. Occasionally
copper seems to be visible through the tinlead.
In general I think this is a very professional boardshop, but (being
not an expert) I don't know what to think about their HASL-process. I
hope someone on this great forum is willing to give me some input on
my
findings, in terms of good or bad, or possibilities for improvement:  

Machine: Quicksilver SM, vertical HASL, 250 kg solderpot, no preheat

Time between microetch (drying) and fluxing can be up to two hours

Solder pot temperature set to 255 °C

Leveling is done is such a way that the solder is as flat as possible,
although the design of the airknives causes a big difference betweeen
the two boardsides. With XRF we measured a thickness of only 0.4
microns
on BGA-pads, with about 3 microns on similar pads on the other
boardside.

Water-based flux from an open tank, without any composition control,
but tank is replaced every 24 hours. 
Solder is replaced every 6 months, but except for copper contamination
no composition-check is ever done. 
When copper is above 0.3 % the dross is skimmed off to assure that
copper content stays below 0.35 %.
Throughput of the machine is about 700 panels per day. 

Daan Terstegge
Thales Communications
Unclassified mail
Personal Website: http://www.smtinfo.net 

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