Hi Graham - in the words of Sir Doug, "it depends"! Under most situations, that thin of underfill will have no influence on the solder joint integrity. However, a specific component construction may not be happy with any underfill on its top causing issues. The simple way to avoid the question is to not allow underfill on the top of the BGA or CSP. I can't speak for a flip chip as I don't have any underfill experience in that realm. Dave Graham Collins <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 06/04/2009 11:20 AM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to [log in to unmask] To [log in to unmask] cc Subject Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal Absolutely. If material interferes with installing heatsinks, it's unacceptable. But that would be true also of other methods like corner bonding. My question: would a thin film of underfill material, say a thou or two, on a small section (say 15% of the top area) of a BGA have any impact to reliability? I am not talking about having big globs of the stuff on top (although I still wonder how that would influence reliability). In terms of impacting reliability, I think a more important criteria would be that the underfill be even volume on each side (so the part would be underfilled reasonably symmetrically). Same size fillets on opposing sides. regards, - Graham -----Original Message----- From: [log in to unmask] [mailto:[log in to unmask]] Sent: Thursday, June 04, 2009 1:12 PM To: [log in to unmask]; Collins, Graham (FN) @ ESI Subject: RE: [TN] Underfill Workmanship Pass/fail Criteria Proposal Too much material over the top of the component many add uncalculated thickness when installing a heat sinks. Vic, -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Collins Sent: Thursday, June 04, 2009 11:01 AM To: [log in to unmask] Subject: Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal How? And to what extent?? Would a tiny bit of underfill on one corner hurt the reliability? Are you talking about big lumps of underfill, or a thin skin? The underfill we use is pretty thin, runs everywhere if allowed to, and will form a thin coating on top if it gets there. regards, - Graham -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D. Sent: Thursday, June 04, 2009 12:41 PM To: [log in to unmask] Subject: Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal Yes, having some on top of the component hurts the reliability. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Collins Sent: Thursday, June 04, 2009 10:27 AM To: [log in to unmask] Subject: Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal Hi Bev Why would material on the component top be considered a defect? Process indicator I can see, but does it impact reliability? regards, - Graham -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian Sent: Thursday, June 04, 2009 12:07 PM To: [log in to unmask] Subject: [TN] Underfill Workmanship Pass/fail Criteria Proposal TechNetters, OK after speaking to a couple of industry friends, this is what we have come up with. I will leave it to them to speak up and identify themselves, if they wish. I have written this up in IPC-A-610 format and have tried to cover all situations for Class 2 and 3 products in particular. If we can nail this, I would like to present this to the IPC as the first IPC draft doc essentially hammered out by out TechNet community. Comments readily accepted! Bev RIM Workmanship Standards for BGA and CSP Underfills Target - Class 1,2,3 * Component requiring underfill completely underfilled with a good fillet all the way around, the fillet just approaching the maximum component body height, completely cured, no encroachment onto other components and no voiding whatsoever Acceptable - Class 3 * At least 50% fillet height up the side of the component body * Small pin holes and voids are permissible provided they do not exceed 5% of fillet surface area and have a maximum diameter of 0.5 mm (0.020 inches). Acceptable - Class 1,2 * Component requiring underfill underfilled such that all balls are covered, but no evidence of an exterior fillet, no encroachment onto other components and no voiding whatsoever * Component requiring underfill underfilled such that all balls are covered, with or without an exterior fillet, no encroachment onto other components and only small voids, not touching any solder joints * Component requiring underfill underfilled such that all balls are covered, with or without an exterior fillet, no encroachment onto other components and even large voiding, but not touching any solder joints * A void or voids less than or equal to 50% around the perimeter of one or more solder joints Defect - Class 1,2,3 * Underfill completely missing from components where it is required * Underfill not completely covering all the peripheral solder joints * Voiding such that a void traverses the distance between two or more solder joints under the array device requiring underfill * A void or voids more than 50% around the perimeter of one or more solder joints * Material extending on to the top of the BGA or CSP * Uncured material Special Conditions - Class 1,2 * Encroachment onto other components, but meeting all other criteria above for target or acceptable conditions will be dealt with as a pass/fail on a case-by-case basis --------------------------------------------------------------------- This transmission (including any attachments) may contain confidential information, privileged material (including material protected by the solicitor-client or other applicable privileges), or constitute non-public information. 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