Bev I am very sorry but I did not send my old text as I agreed after my trip, I just could not find it as it dated back to May 2001. I never sorted out the images for the flip chip and uBGA from my libarary for the posters/wall charts. The draft text is below which I actually found on line at SMTNet Forum with three comments see link: http://www.smtnet.com//forums/index.cfm?fuseaction=view_thread&CFApp=1&Threa d_ID=1600&#Message6706 Here is a draft visual inspection guide for underfill, please pass this on to the relevant people for any comments or suggestions. I am currently working on the pictures to go with the reference guide. Flip Chip/uBGA Underfill Visual Standards The aim of this document is to produce some draft text and then select photographs to make up a draft visual standard for inspection. There is also a need to produce some reference material for C Scan images. The following images provide a guide to the inspection requirement after the underfilling operation. They may also be applied after curing of the underfill. CLASSIFICATION OF QUALITY STANDARDS During the assessment the following classifications, which are pictorially illustrated, should apply: SATISFACTORY This is a satisfactory condition which should be achieved and used as the standard for manufacture. ACCEPTABLE This condition represents the maximum acceptable departure from the "Satisfactory" condition. Examples within this limit of deviation will not require reworking. Individual clarification accompanies each example illustration. Consideration should be given to modification to the process materials or conditions. UNACCEPTABLE This applies to an unacceptable condition which should not be reworked without the cause of the fault being established. Rework may be possible after assessment of the fault and corrective action taken on the process. Flip Chip/uBGA Underfill Visual Standards Satisfactory The underfill should be visible at the edge of the device and extend completely around the perimeter. Satisfactory The underfill should be visible on all four sides, there may be evidence of more material on one or two sides to aid complete filling of device base. Satisfactory The underfill if by design should be visible on the side of the device and reach a minimum height of 25% of the thickness of the package. Satisfactory The base of the device should be completely filled with no evidence of voids in the underfill or solder joints being visible around the perimeter of the device. Satisfactory Curing of the underfill material should be compared with the reference colour standards. Evidence of colour change illustrates a correctly cured sample. Acceptable Flow out of underfill from the device is acceptable provided that it does not completely cover any solder joints. Flow out on to test points, through holes is unacceptable and needs to be reworked and the process modified. Acceptable Small bubbles in the surface of the underfill fillet is acceptable provided that no solder joint is visible. Acceptable Evidence of a needle dispense pattern around the device is acceptable, the width of the pattern should be kept to a minimum. Acceptable The underfill if by design should be visible on the side of the device and reach a height of no less than 20% of the thickness of the package in the centre of any side. Acceptable Underfill fillets which are not visible on the side of the device are not rejectable, however modifications to the dispense process should be made Unacceptable There is no evidence of underfill on the top side of the device Unacceptable Curing of the underfill should be compared with the reference colour standards. No evidence of colour change is unacceptable. Unacceptable The underfill is not visible along the complete side of any device Unacceptable Solder joints are visible without underfill on the side of the device Unacceptable There should be no evidence of underfill flowing out through holes under the device. Unacceptable After curing there should be no visual evidence of cracks between the device surface, underfill or board. Unacceptable There should be no evidence of damage to the board or device caused by contact with the dispensing needle or height sensor. When using CSAM to asses the underfilling/curing process the following criteria may apply: Satisfactory Underfill is complete and there is no evidence of voiding between the device and the board. Acceptable Underfill is complete and there is evidence of small voids of less than 50% of the solder bump diameter. There is no evidence of voids around solder joints. Unacceptable After curing there should be no evidence of cracks between the device surface, underfill or board. Unacceptable Underfill is incomplete and there is evidence of voids around or between the solder joints Unacceptable Underfill is complete but there is evidence of voids which are larger than 50% of the solder bump Unacceptable Underfill filler shows evidence of separation or uneven flow and will expansion matching and affect the long-term reliability. Draft Produced by Bob Willis 28/5/2001 Issue 4. Bob Willis 2 Fourth Ave, Chelmsford, Essex, CM1 4HA England Tel: (44) 1245 351502 Fax: (44) 1245 496123 Mobile: 07860 775858 www.ASKbobwillis.com www.SolderingStandards.com PCB Design for Manufacture & Assembly Workshop 15th October www.ASKbobwillis.com PCB Inspection & Quality Control Workshop 3rd November www.ASKbobwillis.com/faworkshops.pdf Book Bob's "Step by Step Failure Analysis Workshop" 4th November www.ASKbobwillis.com/faworkshops.pdf -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian Sent: 04 June 2009 21:45 To: [log in to unmask] Subject: Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal Bob, This is weird. You are the second TechNetter to ask for the draft document, which I posted on TechNet this morning at 11:07 AM EDST. Here it is again. 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 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of bob wettermann Sent: Thursday, June 04, 2009 4:42 PM To: [log in to unmask] Subject: Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal Dear Richard: Pls send the proposal on to us. We perform underfill rework and this issue presents itslf fairly frequently. Thanks Bob Wettermann [log in to unmask] Bob Wettermann PH 847-767-5745 --- On Thu, 6/4/09, Stadem, Richard D. <[log in to unmask]> wrote: From: Stadem, Richard D. <[log in to unmask]> Subject: Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal To: [log in to unmask] Date: Thursday, June 4, 2009, 1:10 PM I reviewed the proposed items for the standard and I think it looks great. I have sent it to several other people directly involved in BGA, CSP, and flipchip underfill at various companies in Minnesota for their review and will pass on their comments as well. Thank you for doing all of this work. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian Sent: Thursday, June 04, 2009 11:43 AM To: [log in to unmask] Subject: Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal The doc we are discussing is only for CSPs and BGAs. I did not want to try and tackle too much, especially something that: a) I don't know about b) Has been around a lot longer and might already have a set of pass/fail criteria Bev RIM -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman Sent: Thursday, June 04, 2009 12:40 PM To: [log in to unmask] Subject: Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal 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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