I think I see where you are coming from. I think your intuited concern is about relatively few big balls sitting on a pad with not enough flux. All stencil grade solder pastes are about 50% solder/50% flux by volume and this doesn't change on or by being printed [on different pad sizes]. Smaller apertures might require smaller balls and thinner stencils, but a type 4 powder paste is still around 50% v/v. Specified weight per cents will vary according to alloy to maintain the 50/50 volume relationship; and slightly with powder size to maintain rheology. This latter is to accommodate the change in packing densities of different powder sizes. Powder size is determined by aperture size. As a rule of thumb select powder to have 6 or more (largest size) balls to line up across minimum pad. T4 powder has a higher surface area than T3, but if you are buying your paste from a recognized supplier this will not translate into higher oxide content. If going to finer powder/smaller apertures then you will need to also reduce stencil thickness to maintain wall height to aperture ratio. Hope this helps. Regards Mike -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Amol Kane (Asteelflash,US) Sent: Thursday, August 16, 2012 8:34 AM To: [log in to unmask] Subject: [TN] CSP BGAs Dear Technetters, We are going to be assembling some lead-free 1.6x0.8 mm micro BGAs with 0.5mm pitch and 0.17mm dia board pads. Anybody else have experience with this small a package?....I am concerned that there won't be sufficient flux in the tiny solder deposit to clean the oxides during reflow, leading to graping and/or head in pillow situation. Do I need a dip fluxer for the part to do a flux only attachment, or to augment the amount of flux in the solderpaste-solder bump system? I am told I have no time to do DOEs to determine stencil and reflow parameters, so I am turning to technet for help.....any thoughts? Regards, Amol ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________