We began using gold over nickel PCBs on a trial basis over 2 years ago. It was so successful that we now have all boards with mixed or all SMT content made that way. We have always used no-clean fluxes. The finish was available from our PCB supplier at no extra cost from previous HASL finish. Actual process spec is 3-5 microns nickel with 0.05-0.1 microns gold over. Benefits are: * maximally flat finish which is vital for fine pitch SMT * error free fiducial recognition on assembly machines * good contrast between pasted and no-pasted lands which aids inspection * long shelf-life Nigel Burtt Production Engineering Manager D - European HQ Email: [log in to unmask] Tel: 01793 842132 Fax: 01793 842101 ----Original Message----- From: Paul Klasek [mailto:[log in to unmask]] Sent: Tuesday, August 11, 1998 1:42 AM To: [log in to unmask] Subject: Re: [TN] Gold Immersion and planarity Hi Matthew Muddy waters all right ; don't paint them too rosy ; No Clean on gold is tight window . Matthew , myself being a great fan of NiAu versatility ; I still wouldn't say it's wetability is "far superior than HASL's" . However without dissecting it over measurability and applied methods and standards ; something must have prompted you (usually folks struggle on NC gold) ; if you have that good supplier of immersion I'd appreciate if you'd let me know ; in the process of establishing periodic benchmark system for immersion finish presently . Thanks a lot Matthew Paul Klasek http://www.resmed.com > ---------- > From: Matthew Park[SMTP:[log in to unmask]] > Sent: Saturday, 8 August 1998 9:18 > To: [log in to unmask] > Subject: Re: [TN] Gold Immersion and planarity > > Dhawan, > > So, you try to skip all research headaches and jump right into the > muddy water. Check Enthone and kester web sites. They have > many excellent technical articles written on the subject of OSP's > - www.kester.com > - www.enthone-omi.com > > Also check July 1997 & August 1998 editions of Printed Circuit > Fabrication for OSP and electroless immersion gold/nickel > articles. If you don't have them, name your fax, I will try my best > to > fax them on Monday. > > If you plan to use no-clean in near future, I recommend > immersioin gold/nickel finish coating. This is a drop-in > replacement for HASL boards. You don't have to fiddle > around with the existing process. Wettibilty of gold is far superior > than HASL and solder joint fillet formation is far better. > One major solder appearance change from HASL is all solder > joints are dull-looking. Solder joint embrittlement due to too > much gold content (usaully 3/5% more) are unfounded. > Immersion gold/nickel provides consistent gold thickness of > 1um. > > One problem you might encounter (depending upon who your > board vendor is for immersion gold) is gold fall-out around SMT > pads. This could cause shorts especially for QFP pads. Gold > fall-out (fine gold dusts) is usually caused by too much plating. > The problem can easily fixed by fine-tuning gold plating process > by the board vendor. > > OSP coated board provides the same or better flatness than > gold. But the manufacturing process requires some fiddlings > and the handling of boards are more sensitive. It provides a > superior solder joint shininess and less intermetalic and cold > joints. This is because there are no oxidized and contaminated > solder from HASL. > > Some of issues you might tackle when using OSP coated > boards: > > Watch out how many heat cycles a product go thru, and boards > should be assembled and completed within a limited time. > Don't leave them out on the floor too long when they have to go > thru next assembly and heat cycle. I guess I am talking about a > few days.. Non or de-wetting could be a problem if not > processed within a given time. > > Cleaning of mis-printed board could cause non-wetting problem > as well. This tends to remove a fraction of OSP coating. 0.35um > thickness is indeed thin. > > Solder filling of thru-hole in the wave is another issue. It will > never get filled fully the way HASL coating. Usually solder wicks > up to about 50% or 75% of hole. This is acceptable under IPC > 600 class 2 and 3. > > You also have to deal with exposed copper area. I don't think it > will be a quality issue. > > Training of assembly people for the proper handling of OSP is > also important. > > More active flux (Water-soluble) works better with OSP, and there > are no-clean flux formulated for OSP. I tested one no clean flux > type but the result isn't better than the one I am using. > > I guess I am telling OSP is not a drop-in replacement for HASL > > regards > Matthew Park > SMT Manufacturing Engineer > NII-Norsat International Inc. > Surrey, BC. > > sorry I can not help you with surface flatness. I don't think there > is any guideline for that. But the pad surface level should be > within a twice thickness of leaded pin for QFPs. > > >>> "Dhawan, Ashok" <[log in to unmask]> August > 7, 1998 1:48 pm >>> > For fine pitch devices 15.7 mils and small chips 0603 ,do we > have any > IPC standard stating that what kind of surface leveliing /planarity > required for placement of FPDs and 0603/0402 chips.Even > accurate > placement can go offline once the surface is not flat. the situation > is > worse when we are trying to place 0603 components on glue > dots. > > > Also, there are no. of options for HAl alternatives . We are > comparing > gold immersion and OSPs.Our circuit boards are having fine > pitch devices > extendable to 12 mils QFPs and 50/60 mils BGAs and chips > down to 0402 > package size.We also intend to implement No-Clean process in > near > future. We have limited experience with Au immersion/Ni > electroless > and OSPs. > What are views of experts who had some point of time decided > course of > action. What you think we go for?We want to go for process > where we do > not have to modify /readjust our current process based on water > soluble > soldering. Pro and Cons? > > Not to mention that I consider technet as my vital tool for problem > solving. I will appreciate comments on this asap as I am running > out of > time and our process meeting is scheduled on Monady morning. > > thanks > > ################################################################ > TechNet E-Mail Forum provided as a free service by IPC using > LISTSERV 1.8c > ################################################################ > To subscribe/unsubscribe, send a message to > [log in to unmask] with following text in the body: > To subscribe: SUBSCRIBE TechNet <your full name> > To unsubscribe: SIGNOFF TechNet > ################################################################ > Please visit IPC's web site (http://www.ipc.org) "On-Line > Services" section for additional information. > For technical support contact Hugo Scaramuzza at > [log in to unmask] or 847-509-9700 ext.312 > ################################################################ > > ################################################################ > TechNet E-Mail Forum provided as a free service by IPC using LISTSERV > 1.8c > ################################################################ > To subscribe/unsubscribe, send a message to [log in to unmask] with > following text in the body: > To subscribe: SUBSCRIBE TechNet <your full name> > To unsubscribe: SIGNOFF TechNet > ################################################################ > Please visit IPC's web site (http://www.ipc.org) "On-Line Services" > section for additional information. > For technical support contact Hugo Scaramuzza at [log in to unmask] or > 847-509-9700 ext.312 > ################################################################ > ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################ ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################