Any flux residues are risky. Where we have rigorous MIL/SPACE requirements, we perform high pressure liquid cleaning, "no" residues are allowed under the BGAs or elsewhere. (Getting 100% cleanliness under a superBGA isn't easy.) Where ionic residues are left, enclosed water droplets can start parasitic leakage currents or even migration and corrosion. After the cleaning and bake out, we apply conformal coating. Room conditions are not quite safe either..rare but occasional, chemical processes can self-generate microscopic amount of water. If mother nature is in her worst mode, she can tunnel hydrogen just straight through 1 mm thick Kovar package walls (hermetic packages)and, depending on what's on inside, create water there. When we got such reports from NASA (think it was), they were classified and locked in! Today, no problems, we have water absorbants screenprinted on the inside of the lids. Inge -----Ursprungligt meddelande----- Från: Steve Kelly [mailto:[log in to unmask]] Skickat: den 15 april 2008 22:30 Till: 'TechNet E-Mail Forum'; 'Hfjord' Ämne: RE: [TN] SV: [TN] Possible flux contamination issue Hi Inge, No you are correct- the bias voltage is after the damp heat test not during. The problem is we are failing the test sometimes (high resistance short) - and when we grind off the BGA connector we see flux residues on the connector side but not on the flex. So my next question would be if the connector BGA balls are already assembled with no-clean is there any concern of assembling the connector onto the flex with no-clean - I cannot think of any. At the end of the day this product sits in an air-conditioned room. Thanks. Steve Kelly -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Hfjord Sent: April-15-08 2:13 PM To: [log in to unmask] Subject: [TN] SV: [TN] Possible flux contamination issue Why this extreme requirement? BGA's use to be signal processing units, which is normally maximum 48 VDC. If you mean 250 Volts AFTER the environmental test and at room conditions, I think it's reasonable, but 250 Volts bias under test condition is horrible, not to say madness. /Inge -----Ursprungligt meddelande----- Från: TechNet [mailto:[log in to unmask]] För Steve Kelly Skickat: den 15 april 2008 14:42 Till: [log in to unmask] Ämne: Re: [TN] Possible flux contamination issue Good Morning, I need to ask some more questions on this thread. One of the reasons our customer went to a water soluble paste was the high voltage/damp heat test requirement on the finished assembly. The test requirement is 1000 hours of damp heat test at 85C/85RH. The voltage requirement is 250 volts. BGA pad spacing is .050. The customer was concerned about passing this test. Regards Steve Kelly Steve Kelly PFC Flexible Circuits Limited PH: (416) 750-8433 Fax: (416) 750-0016 Cell: (416) 577-8433 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Kelly Sent: Monday, April 14, 2008 1:58 PM To: [log in to unmask] Subject: Re: [TN] Possible flux contamination issue Thanks everyone for the help. Regards Steve Kelly -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis Sent: April-11-08 11:50 AM To: [log in to unmask] Subject: Re: [TN] Possible flux contamination issue 24 years ago (yes 24!), I gave a paper at InterNepcon, in Brighton, UK, entitled "Contamination on Components and Small Assemblies". I no longer have a copy, but I'm fairly sure I evoked the need to have all the components supplied clean to avoid just this kind of problem. Brian Steve Kelly wrote: > Good Morning, > > We are assembling a BGA connector onto a flex circuit. The BGA has leaded > balls and the BGA manufacturer uses a no-clean process to attach the balls > to the connector and does not clean afterwards. > > When we assemble the BGA connector to the flex we use water soluble paste > and then we clean. After damp heat cycling we have seen some shorts. When we > take off the connector we see flux residues on the underside of the > connector but not on the flex. So my question is - what are the concerns > about mixing no-clean and water soluble? Is the failure likely due to > inadequate cleaning or is there something else I should be concerned about. > I realize this is probably not the way it should be done but some days you > just do what the customer wants - good or bad. Thanks in advance. Steve > Kelly > > > > Steve Kelly > > (416) 750-8433 (work) > > (416) 750-0016 (fax) > > (416) 577-8433 (cell) > > > > > --------------------------------------------------- > 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 ----------------------------------------------------- --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 -----------------------------------------------------