Okay. Some things are new. Some things people did not like. I have a new version (version 3) below. I have made changes in CAPITALS, since colors won't show up in TechNet. Let me know what you think. I can't say I'm thrilled with some of the things I have written here, but hey, it should lead tot some healthy discussion if nothing else. There is also a section at the end on testing, which I can't remember if I added before or not. Too lazy to go back and look. Bev RIM Workmanship Standards for BGA and CSP Underfills For general inspection of all circuit packs coming down a production line, apply only the portions of this document that can be performed visually to underfilled, uncovered CSPs and BGAs or those same types of components under fence and lid RF shields. The visual inspection rules do not apply to CSPs and BGAs for general production under single piece RF cans. This would require destruction of all product. However, all the rules apply for process development/product qualification where one is willing to sacrifice finished circuit packs to gain knowledge of the acceptability of the overall quality. 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. * Total void area, irrespective of location, as a percentage of component area shall be equal to or less than 10%. * A void or voids less than or equal to 50% around the perimeter of one or more solder joints, including in an outer row. * Voids greater than 50% around inner row solder joints. * Solder joints with voids completely surrounding individual solder joints and/or voids connecting two solder joints make up less than 10% of the total number of solder joints of the component. This rule only applies to inner row solder joints (E). Defect - Class 3 * Less than 50% fillet height up the side of the component body * Small pin holes and voids exceeding 5% of fillet surface area and/or have a maximum diameter of greater than 0.5 mm (0.020 inches). 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 OUTER ROW solder joints (DELETE under the array device requiring underfill) * A void or voids more than 50% around the perimeter of one or more OUTER ROW solder joints * Material extending on to the top of the BGA or CSP * Uncured material * Underfill interfering with proper placement of a heatsink or other mounted or mechanical devices or would interfere with the assembly * There should be no evidence of underfill flowing out through holes under the device. * After curing there should be no visual evidence of cracks between the device surface, underfill or board. * There should be no evidence of damage to the board or device caused by contact with the dispensing needle or height sensor. * Underfill filler shows evidence of separation 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 Methods of Test Unfortunately the presence of RF cans make it impossible to do the testing by acoustic microscopy for components under cans. Other possibilities and their advantages and disadvantages: Method Advantages Disadvantages Prying Fast, easy, can be done by anyone, checks whole area under component at once Misses embedded voids that don't reach the underfill/component interface Vertical Cross-sectioning Finds buried voids Requires lab staff, only finds voids in the particular plane sectioned, unless grind further (very time consuming) Horizontal cross-sectioning Finds buried voids, checks whole area under component Requires lab staff, very time consuming --------------------------------------------------------------------- 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. Any use of this information by anyone other than the intended recipient is prohibited. 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