Hi Pratap! I respectfully suggest you have some misinformation on gold and
soldering. I would offer the following information:
"Technically - gold in solder joint should be avoided in general. 1-3
micro inch gold will be dissolved during wave solder if wave contact
time is 5-8 seconds. It will depend upon wave width, conveyor speed and
whether the machine is single pot or dual pot."
*** Gold will rapidly diffuse into molten solder at a rate of approximately
40 microinches per second (1umeter per second) based on data from Bader and
Klein Wassink. So having 1-3 microinches of gold on a circuit board or
component is a nonissue. An old rule of thumb for thru hole soldering is
that you avoid gold embrittlement issues provided the gold plating
thickness is less than 100 microinches (keep in mind- 200C temperature,
large solder pot = large solder volume and solder wave contact of
approximately 2-3 seconds). For surface mount soldering you have to
calculate the amount of solder volume, know the amount of gold on the
leads, and see if you are going to exceed approximately 3-4 weight percent
gold in the solder joint (brittle gold/tin intermetallic formation is a
function of the amount of gold in the solder).
"Now 1-3 micro inch gold will be porous, especially on PTH copper which
is typically rough, so you will have exposed copper. Again depending
upon how long you store your PCBs and in what type of environment, there
may be solderability questions."
*** A 1-3 microinch thick electrolytic gold plating will be porous but a
1-3 microinch immersion gold surface finishes are not porous due to the
nature of the immersion plating process. Using a scanning electron
microscope you can look at a properly controlled immersion gold surface and
see pore free coverage.
Take a look at the TechNet archives - there is some great information on
gold embrittlement and gold finishes from past discussions.
Dave Hillman
Rockwell Collins
[log in to unmask]
pratap <[log in to unmask]>@IPC.ORG> on 03/02/2001 05:59:27 PM
Please respond to [log in to unmask]
Sent by: TechNet <[log in to unmask]>
To: [log in to unmask]
cc:
Subject: Re: [TN] Soft Gold Over Copper
Bill,
Ask the customer for data on the (a) process, (b) solder joint
quality/reliability, (c) solder pot maintenance and (d) guaranteed gold
thickness, and he will back off......( just kidding).
Technically - gold in solder joint should be avoided in general. 1-3
micro inch gold will be dissolved during wave solder if wave contact
time is 5-8 seconds. It will depend upon wave width, conveyor speed and
whether the machine is single pot or dual pot.
Now 1-3 micro inch gold will be porous, especially on PTH copper which
is typically rough, so you will have exposed copper. Again depending
upon how long you store your PCBs and in what type of environment, there
may be solderability questions.
Finally, controlling gold thickness is tricky, have seen it vary upto 30
micro inches. This much gold will cause brittle joints. People set up
processes to remove gold from leaded components to avoid this type of
problem. Also consider the case when you have to wave solder a gold
leaded pin-grid-array which will add to the gold dissolution problem in
PTH joint.
pratap
www.rampinc.com
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET
Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases >
E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
---------------------------------------------------------------------------------
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------
|
