Amol, Probably the only other choice you have is to grind off the package gradually and inspect the underfill coverage. Regards, Vladimir SENTEC SENTEC 11 Canadian Road, Unit 7. Scarborough, ON M1R 5G1 Tel: (416) 899-1882 Fax: (905) 882-8812 www.sentec.ca -----Original Message----- From: "Kane, Amol (349)" <[log in to unmask]> Date: Tue, 22 Sep 2009 07:30:22 To: <[log in to unmask]> Subject: Re: [TN] Acoustic Microscopy for Under fill Coverage Guys, thank you for all the interest in the subject. Lots of good information indeed. Yes, I did talk to Sonoscan and they pretty much corroborated what most people here are saying in that there are too many interfering layers to effectively look at underfill coverage and any voids or dewetting to the board/component surface. So let me ask this...HOW CAN I look at a underfilled BGA and determine how good/bad my process for underfilling them is? (I am setting up a new process for manually underfilling BGAs). I want to determine if the underfilling technique used is consistently producing good results across BGAs and if the board cleanliness level is sufficient to ensure complete wetting and spread underneath the BGA. I am working with test vehicle now, but the actual boards will be used in a shock application. Any established standards (formal or informal) out there? The bottom line is that I need to be able to show the customer that the process produces underfilled BGAs with minimal voiding and dewetting. Werner, are the critical areas (i.e. the corners) the same for shock/vibe as for more gradual stresses on a BGA? Thanks, Amol -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman Sent: Monday, September 21, 2009 11:12 PM To: [log in to unmask] Subject: Re: [TN] Acoustic Microscopy for Under fill Coverage Hi Werner -- there have been a number of examples in which a component construction interaction of a "partial underfill" has resulted in increased degradation of the solder joint integrity in comparison to a "complete underfill" case. Dave Werner Engelmaier /* <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 09/21/2009 06:17 PM 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] Acoustic Microscopy for Under fill Coverage Hi Guys, The premise of the original question was by inference that completeness of the underfill coverage is necessary. Would not be an underfill 'ring' covering the first 5 or so 'SJ squares' accomplish what is desired?better reliability? That would make this discussion academic. Werner -----Original Message----- From: Vladimir Igoshev <[log in to unmask]> To: [log in to unmask] Sent: Mon, Sep 21, 2009 6:47 pm Subject: Re: [TN] Acoustic Microscopy for Under fill Coverage C-SAM does do a beautiful work on flip-chip packages and of cause not in the transmission mode. Regards, Vladimir SENTEC SENTEC 11 Canadian Road, Unit 7. Scarborough, ON M1R 5G1 Tel: (416) 899-1882 Fax: (905) 882-8812 www.sentec.ca -----Original Message----- From: "David D. Hillman" <[log in to unmask]> Date: Mon, 21 Sep 2009 17:30:36 To: <[log in to unmask]> Subject: Re: [TN] Acoustic Microscopy for Under fill Coverage Hi Bev - I have attempted to use Acoustic Microscopy for underfill coverage on BGAs and as other folks have detailed, the number of interfaces and structures cause significant signal reflection problems making analysis very difficult. Some specific focused interface examination efforts can be conducted but are still very difficult to analyze. Dave Hillman Rockwell Collins [log in to unmask] Bev Christian <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 09/21/2009 05:16 PM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond=2 0to Bev Christian <[log in to unmask]> To [log in to unmask] cc Subject Re: [TN] Acoustic Microscopy for Under fill Coverage John and others, But wouldn't it be even worse trying to use transmission mode because of the nature if the circuit board underneath the component (copper barrier(s), glass fiber bundles and epoxy? Nobody from Sonotek or Sonoscan on TechNet? Bev ----- Original Message ----- From: John Burke <[log in to unmask]> To: 'TechNet E-Mail Forum' <[log in to unmask]>; Bev Christian Sent: Mon Sep 21 18:00:16 2009 Subject: RE: [TN] Acoustic Microscopy for Under fill Coverage Not a discontinuity as such just an interface, and you are right, the signal reflections will be from every interface, so for a BGA (without a lid) the interfaces will be as follows: 1 Liquid to top of package molding compound 2 Molding compound to silicon 3 Silicon to die attach 4 Die attach to substrate 5 4 or so interfaces in the substrate itself (copper to substrate pre-preg) 6 Substrate to under fill (or NOT!) Depending of the acoustic impedance between the Material travelling from/Material travelling to, more or less ultrasound energy will be reflected at each of the interfaces. Of the layers above I believe that the strongest reflection will be from level 6 above. It is 30 years since I last played with non destruct testing using ultrasonics, but I would bet from my experiences then that you would do far better using through transmission for this scenar io rather than reflected signals due to Bev's comment, particularly due to the substrate interface reflections masking the ones between the package and the under fill. John Burke (408) 515 4992 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian Sent: Monday, September 21, 2009 2:07 PM To: [log in to unmask] Subject: Re: [TN] Acoustic Microscopy for Under fill Coverage Since when can an acoustic signal punch through a BGA? I know you can do if for flip chips, but aren't there too many density discontinuities for CSPs abd BGAs? Bev ----- Original Message ----- From: TechNet <[log in to unmask]> To: [log in to unmask] <[log in to unmask]> Sent: Mon Sep 21 14:40:48 2009 Subject: [TN] Acoustic Microscopy for Underfill Coverage Anybody know a good lab in the North East that does acoustic microscopy? I need to verify under fill coverage under BGAs. Thanks, Amol WARNING: Export Control This document may contain technical data within the definition of the International Traffic in Arms Regulations (ITAR), and subject to the Export Control Laws of the U.S. Government. Transfer of such data by any means to a foreign person, whether in the United States or abroad, without proper export authorization or other approval from the U.S. Department of State is prohibited. CONFIDENTIALITY NOTICE: This e-mail, and any attachments, is for the sole use of the intended recipient(s) and may contain information that is confidential and protected from disclosure under the law. 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