John,
I am looking at Table 3-2 in IPC-6012A with Amendment 1 and the maximum
amount of gold allowed now is 0.8 µm so I am not sure what you are saying
below in the sentence "More recently it has been recommended that the Class
3 maximum allowance be increased to a value of 0.8 µm [31.5 µin]."  Anyway,
even though I agree thinner is better, I see no problem with leaving it as
it is and letting the customer specify the maximum they want on their
fabrication drawing, if they want less.
Scott

----- Original Message -----
From: "John Perry" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, September 27, 2002 6:58 PM
Subject: [IPC-600-6012] Max Allowance of Gold on Areas to Be Soldered


Colleagues,

In building the IPC-6012B we are making changes to Table 3-2 for Final
Finish Requirements - your disposition on the following is requested:

At Expo, at the request of the 4-14 Plating Subcommittee chaired by George
Milad, it was recommended that for Class 1, 2 and 3 product, the maximum
allowable thickness of gold on areas to be soldered (identified in the table
as Row GS) would be 0.45 µm [17.72 µin].


More recently it has been recommended that the Class 3 maximum allowance be
increased to a value of 0.8 µm [31.5 µin].


The con's offered against this indicate that in the usage of electrolytic
gold plating finish on solderable areas, heavier thickness may not be better
as it can lead to embrittlement of the solder joint.

The pros offered for the increase indicate that in many cases involving
military product, there are two main issues, solderability and
embrittlement.  Some task group members contend that solderability can be a
major issue since military product may not be used for 1 -2 years after
product has been manufactured, whereas many commercial products built are
potentially used right away.  The second issue of embrittlement, however,
many not be so much of an issue - some task group members have calculated
that the percentage of gold in solder, in cases of 30 µin depositions, is
less than 4% and that gold embrittlement is not really a problem.  Hence an
increase in thickness, in favor of long term solderability, is desired.

What maximum thickness value for Class 3 can this task group agree is
appropriate for IPC-6012B?

Thanks,

John Perry
IPC