Thank you Ed.  And thanks to the many who offered advice and suggestions 
both on line and off line.  Much appreciated.  Helluva resource this group 
is.

Doug Pauls




Edward Mines <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
06/14/2007 10:59 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Edward Mines <[log in to unmask]>


To
[log in to unmask]
cc

Subject
[TN] black light intensity measurement






Doug-
  You ask an interesting question. I don't believe there are any standards 
regarding the intensity of UV light for inspection of conformal coatings. 
 
  Before working for HumiSeal I worked for Polychrome, then one of the 
bigger manufacturers of presensitized printing plates. The photosensitive 
coatings on these plates are exposed with high intensity lamps in a vacuum 
frame. Sometimes it was necessary to calibrate the exposure units and we 
had a device we called a "puck". At least some exposure units use UV 
lamps. Some lamps loose illuminating strength over a period of time.
 
  There used to be a company in Chicago (UV Process Supply?) which sold 
everything related to UV curing including these "pucks". Spectronics and 
other manufacturers of UV lamps may know where to get UV intensity 
measurement instruments too. At HumiSeal we had a similar instrument to 
meassure the strength of our UV cure unit.
 
  The intensity of UV is proportional to the distance between the light 
source and the object being illuminated SQUARED  (or maybe even to a 
higher power?). You couldn't look at the light sources we were using at 
both employers.
 
  Now is a good time to mention that the glowing power of the fluorescent 
dye in conformal coatings sometimes declines with age. We suspected that 
this had to do with exposure to light. HumiSeals 1B31 & 1A33 contain a lot 
of fluorescent dye; it's easy to dissolve in the solvents in those 
coatings. It's not so easy to dissolve in some of the other coatings. So 
the glow strength will vary from coating to coating. I think it's 
dependent on coating thickness too.
 
  Don't discount that different operators will count different numbers of 
defects from the same screen. When I worked at Kodak (I got around) we saw 
this many times with microscopists.
 
  Don't get hung up on minute voids in conformal coatings. There are 
breaks in the coating that you can't see - the backs of flat leads, bends 
in flat wire (we called them "knees"). A different material should be used 
for absolute coverage.
 
  Edward Mines BEChE, MEChE 

 
---------------------------------
Take the Internet to Go: Yahoo!Go puts the Internet in your pocket: mail, 
news, photos & more. 

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
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 15.0
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
-----------------------------------------------------