Another factor for immersion plating thickness is the measurement method. Even if same immersion thickness is plated in micro level, the measurement might be different for different surface morphology.

XRF is common measurement method to measure immersion type plating thickness. As I understand, XRF counts number of atoms of plating metal per area and then converts it to thickness by using pre-measured standards. If substrate metal surface is rough, even though plating layer thickness on the surface is same, there will be more atoms per area to count. Result is thicker thickness measurement. It's like more paint is necessary to paint a rough surface, than a smooth surface.

Regards,

Sofu

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of George Milad
Sent: Sunday, May 29, 2005 8:25 AM
To: [log in to unmask]
Subject: Re: [TN] Immersion Plating


 
Immersion plating is  a process by which an ion in solution is reduced to the 
metal at the expense of  the substrate metal being oxidized to the ion. The 
substrate gives up an  electron (oxidized) and the electron is picked up  by 
the deposited metal (reduced).  
This is a  displacement reaction and is self limiting, meaning if no more 
electrons are  supplied the reaction would stop. 
It is a fact  that: 
    *   One can get 8 –10 microinches of immersion gold on Ni (NOT  
RECOMMENDE) 
    *   Immersion tin deposits as much as 50 uins  (ALL THE TIME) 
    *   Immersion Silver thicknesses of 40 uins were measured in some  
instances.
None of these  processes have reducing agents. All are not electroless in  
nature. 
Clearly electrons  continue to be supplied to the reaction after the expected 
coverage was  complete.  
In the case of ENIG  this could be the result of excessive Ni corrosion. The 
electrons don’t have  to be supplied at the point of deposition but may occurr 
at a corrosion site  within the system. 
In the case to  immersion tin, copper dissolution or oxidation may continue 
thru intermetallic  formation that occurs during the deposition process. 
In the case of  silver large ground plane areas may contribute and abundance 
of electrons that  may cause deposition on smaller pads at a faster rate than 
on the larger pads.  The IPC specifies 8 – 12 uins on pad size of 60 X 60 mils 
or  equivalent.

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------