This is good advice, however realize that in some cases a Type 4 paste will print better than a Type 3. If you have very small stencil aperture openings such as for a 0201 or even 0402 chip, or for flipchip components for example, the Type 4 will print much better through the tiny apertures than the Type 3. If you do not need a Type 4 paste, you should be using Type 3 to avoid the non-agglomerated solder fines that do occur. These small solder balls and solder fines occur for two reasons. The first is because the solder has nowhere to go when printed under relatively large flat areas, unlike a leaded component such as a gullwing where the solder can flow up the lead. Chip caps and larger chip resistors do have some solder flow up the endcap termination, but a large amount of solder paste going into reflow under the part may not be able to flow out fast enough, and the result is small solder balls "spit out" from the pressure. This is why components with "belly pads" will always have solder balls under the parts or surrounding the parts if the paste is printed 1/1. An aperture reduction that gives a solder volume of 35% to 50% or even less is needed to provide room for the molten paste to flow. The other reason fines and small solder balls are seen after reflow is because if you use a Type 4 paste your print process must be literally perfect, with no solder paste being printed outside of the metal pad. Even if the paste is compressed slightly due to the component placement pressure, solder fines can be wedged into the opening between the edge of the pad and the edge of the soldermask. These fines will agglomerate together into small solder balls separate from the solder joint. To summarize, your solder paste printing can improve dramatically in terms of perfect bricks of paste if you use a Type 4, but if your printer's alignment, squeegee pressure, speed, and and other parameters cannot be held to extremely tight tolerances, and you don't have good control over the aperture sizes used for a given component, and the pad library is not perfect, then stick with Type 3. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory Sent: Monday, October 15, 2007 9:26 AM To: [log in to unmask] Subject: Re: [TN] Small solder balls Morning Tom, One thing might help is to go to the largest mesh size solder paste that you can use, small mesh sized solder paste tend to have more fines and oxidation that sometimes create solder balls that don't coalesce back into the main fillet. Kind regards, Steve Gregory -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory Sent: Friday, October 12, 2007 4:17 PM To: [log in to unmask] Subject: Re: [TN] Small solder balls Hi Tom! Got your picture posted. It's at: http://stevezeva.homestead.com/files/1206_SolderBall.JPG What kind of soldermask is on the board? LPI or dryfilm? Do you have the mask relieved around the pads by a few mils? I ask that because it almost looks like the solderball is caught right at the edge of the mask sort of... Steve Gregory -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Gervascio, Thomas Sent: Friday, October 12, 2007 1:38 PM To: [log in to unmask] Subject: [TN] Small solder balls Has anyone ever established a baseline of the anticipated frequency of solder balls under chip components? We are doing Space assembly work and the specifications allow for no solder balls. We are using a ROL0 solder paste and cleaning in an inline semi-aqueous cleaner with saponification. What is being rejected are solder balls about a 1-2 mils in diameter that are intermittently trapped under low profile chip caps and resistors. I suspect it is an agglomeration of solder particles in the paste occurring during reflow. I have tried all the usual things- stencil aperture modifications: - homeplates; reverse homeplates(like a bowtie design that reduced the printed pad by 25%); homeplates which are offset 7 mils from the inside edge of the pad: tried reducing hot slump of the paste (changed from 90sec soak between 150-170 sec (per vendor recommendations) to ramp to spike; tried reducing placement force or fudging part thickness. What I am experience I believe is typical of the process but would like some input from my peers. Steve Gregory, can I post a photo on your website- stevezeva.com to show what I am talking about? Thanks Tom Gervascio --------------------------------------------------- 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 -----------------------------------------------------