Guy, I would not recommend straight or co-solvent vapour phase, with or without ultrasound: my experience in this field has been rather negative. It can clean the first few peripheral millimetres great, but it is **extremely** difficult to get right into the centre, even with strong solvents. In particular, we found that the HFC or HFE co-solvent process was not brilliant. The HC solvent got to the middle, fine, but it got stuck there and the subsequent HFC/E cleaning was not good enough to remove this contaminated solvent, retained partially by the balls. Subsequent mechanical removal of the component clearly showed flux residues. Also, the HFC/E losses are greater with the co-solvent process than with a straight VP process: I hypothesise that some solvent mixes with the residual gunge under the components and does not evaporate so readily in the vapour phase/freeboard stages of the process. As these losses are very global-warming, they are environmentally as well as economically undesirable (except for the solvent manufacturers!). I have no ready-made solution to this problem: the best results I've obtained have been experimental in aqueous machines with high volume vertical flooding of the assemblies held at an angle between 15° and 30° from the vertical during the wash stage and then rinsing with vertical fine sprays, which have to be carefully designed that the individual water droplets, arriving at the component-board interface, have an average diameter of under the gap size and sufficient velocity to force its way in and displace the dirty gunge left over from the wash. I found it requires about ten such rinses to be effective, each lasting a second or two, at two or three second intervals, assuming no other components shadow the critical spacing. However, I do not deny that even this is not foolproof. If the real estate permits it, assuming the usual BGA configuration of no balls in the centre, a square cut-out in the board is ideal, but designers like to use this space for fan-outs. HDIS design, allowing in-pad microvias, can overcome this problem. Brian Guy Ramsey wrote: > > We have done some underfill here, very limited quantities will no clean > fluxs. These were 5 mil parts with 2 mil balls. It depends who you talk to > there are advantages to cleaning but there are also problems. We had > reasonable success with the no-clean process. > > IMHO, Even if you get the semi-aqueous solvent under the part, how can you > rinse it out? We use Vigon A200 in out inline cleaner and Kyzen Ionox I3330 > in our batch cleaner. I have seen residue under large BGAs after cleaning. > Both are excellent but the water rinse just won't go into tight places. > > If I was going to try this I think I would experiment with the HFE in a > co-solvent process. But it's expensive, requires modern equipment and good > process monitoring. > > Guy Ramsey > Senior Lab Technician / Instructor > > E-Mail: [log in to unmask] <mailto:[log in to unmask]> > Ph: (610) 362-1200 x107 > Fax: (610) 362-1290 > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]]On Behalf Of Lambert, Katherine A. > Sent: Thursday, August 23, 2001 12:00 PM > To: [log in to unmask] > Subject: [TN] Cleaning under BGAs > > Hi folks, > > We're embarking on something new. We will be assembling boards with BGAs. > Some are small and fine pitch, others are regular pitch but quite large > (40mm square). We will be underfilling them with adhesive. Because we're > underfilling, we have to clean the flux from underneath the parts. We're > using an RMA flux based solder paste. > > Now for the question - how should I clean the flux from under these parts? > Any clues as to which solvent to use? Any ideas on what type of equipment > to use? I have at my disposal an in-line semi-aqueous cleaner and a vapor > degreaser. > > Thanks for any insight. > > Kathie Lambert > Process Engineer > Northrop Grumman > Baltimore, MD > 410-765-9746 > > ---------------------------------------------------------------------------- > ----- > 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 > --------------------------------------------------------------------------------- --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------