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July 2009

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Subject:
From:
Werner Engelmaier /* <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 8 Jul 2009 13:56:48 -0400
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text/plain (139 lines)
 Hi Victor,
For the purpose of my statement, thin is 4 layers and less.
Indeed, PCB thickness plays a big role—thermal expansion mismatch grows with PCB thickness, thicker PCBs require special attention/plating chemistry for good Cu deposits, thicker PCBs require more heat input, thus longer exposure to liquid solder at the surface.


 The 0.8 mils [actually 0.787 mils] comes from Table 3.2 in IPC-6012B [Class 3 is 0.984 mils minimum].
Werner


 

-----Original Message-----
From: [log in to unmask]
To: [log in to unmask]; [log in to unmask]
Sent: Wed, Jul 8, 2009 1:14 pm
Subject: RE: [TN] LF PTH, Knee copper thickness measurement










Werner,

   You state the value of 0.8mil Cu knee thickness for LF solder PTHs.
What is the standard/document that the 0.8mil value was extracted from?
You also make reference to thin PCBs.   What is the associated thickness
value for thin PCBs?   I am old school and think of PCB thickness of
0.068mil.   Is there a relationship between the thickness of the PCB and
the PTH knee value.

Victor,

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /*
Sent: Wednesday, July 08, 2009 11:43 AM
To: [log in to unmask]
Subject: Re: [TN] LF PTH, Knee copper thickness measurement


 Hi Victor,
The 0.8mil Cu standard does not work with Pb-free for 2 reasons except
for thin PCBs. Too thin for the PTH barrel integrity with those large
thermal expansions for any resin with Tg<190C, and too thin for reworks.

Wern
er


 


 

-----Original Message-----
From: Victor Hernandez <[log in to unmask]>
To: [log in to unmask]
Sent: Wed, Jul 8, 2009 8:49 am
Subject: [TN] LF PTH, Knee copper thickness measurement










Fellow ThecNetters:

   Can someone share their experience in measuring the Lead Free PTH
copper thickness at the knee for first pass assemblies and then after 1x
and 2x rework.   This especially true on the solder side of the board.
I have reviewed the IPC-A-600F standard and did not find a
method/technique.   I believe the preferred minimum thickness is 0.5
mils for 2x rework.

Victor,

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