You could very well be right, Guy. I was looking at it from more of a compliance-to-standard viewpoint. -----Original Message----- From: Guy Ramsey [mailto:[log in to unmask]] Sent: Thursday, August 25, 2011 2:04 PM To: 'TechNet E-Mail Forum'; Stadem, Richard D. Subject: RE: [TN] FW: [TN] Gull Wing Lead - no heel fillet Rarely do I disagree with Richard. But, in this case, I do. The strength is in the bond between the lead and the land. The larger the bond area the stronger. Sacrificing the bond area to provide a heel fillet would, I predict, be counter productive, when considering mechanical shock. I do agree with Dewey. Compliance is your friend when it comes to CTE mismatches. So, if we tested with thermal cycling, and if there was a mismatch, a thick joint might outlast a large overlap. So, without a reply, Doug is right . . . it depends. Guy -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D. Sent: Thursday, August 25, 2011 12:28 PM To: [log in to unmask] Subject: [TN] FW: [TN] Gull Wing Lead - no heel fillet -----Original Message----- From: Stadem, Richard D. Sent: Thursday, August 25, 2011 10:01 AM To: 'Amol Kane' Subject: RE: [TN] Gull Wing Lead - no heel fillet Phil explained that his pad does not provide enough length to form either a heel or toe fillet, that is, the pad is the same exact length of the component foot. His question was, is the solder connection along the bottom surface enough, or will there be certain reliability issues without a heel fillet. So my feeling is, if the gull wing component leads can be "re-formed" to slide the foot outwards, perhaps .020" or so, this would allow the heel of the lead to rest inside the pad, and a heel fillet could be formed. While the toe would now overhang the front of the pad, this is redundant as the toe fillet provides very little to the overall finished solder surface of the component lead (the plated inside bottom surface area of the component lead is intended to be the solderable surface, not the unplated oxidized exposed copper edges. That is why the heel fillet is considered to be so important). While this would provide a .020" x "W" smaller planar area for solder wetting, it would be more than offset by allowing the solder volume up the inside of the heel area. Then you would be able to get a heel fillet that is a minimum of either 1 lead thickness in height (class 3) or at least 1/2 the lead thickness (Class 2). -----Original Message----- From: Amol Kane [mailto:[log in to unmask]] Sent: Thursday, August 25, 2011 9:04 AM To: TechNet E-Mail Forum; Stadem, Richard D. Subject: RE: [TN] Gull Wing Lead - no heel fillet Richard, Can you elucidate "I would reform the leads outward to obtain a minimum acceptable heel fillet (1/2 H)"? Thanks, Amol -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D. Sent: Thursday, August 25, 2011 8:54 AM To: [log in to unmask] Subject: Re: [TN] Gull Wing Lead - no heel fillet I would reform the leads outward to obtain a minimum acceptable heel fillet (1/2 H). If the toe fillet is not there anyway, or is redundant, then you have improved the reliability to the equivalent "good" pad dimension. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Bavaro Sent: Wednesday, August 24, 2011 8:39 PM To: [log in to unmask] Subject: Re: [TN] Gull Wing Lead - no heel fillet Thanks Bev. Not under pressure, just surprised anyone would suggest hi rel w/o heel fillets! ----- Original Message ----- From: Bev Christian [mailto:[log in to unmask]] Sent: Wednesday, August 24, 2011 05:08 PM To: 'TechNet E-Mail Forum' <[log in to unmask]>; Bavaro, Phillip @ MWG - TW Subject: RE: [TN] Gull Wing Lead - no heel fillet Phil, First, I am a chemist not a mech eng. Second, I never heard of the Steinburg equation before your e-mail. Third, the companies I have worked for (well the 2 big, reputable ones) built and build class 2 product. That being said, I googled Steinburg equation and came across the abstract below. Sounds to me that I would not be wanting to hang my hat, let alone my product, on an equation, Steinburg or Guinan-Steinburg that is a tad too simplistic. Sounds to me that what you really need is thermal cycling, but my guess is that you are under some time pressure for a decision. I do not envy you. My 2.0242 cents. Bev RIM Shear modulus at all pressures: Generalized Guinan-Steinberg formula Purchase References and further reading may be available for this article. To view references and further reading you must purchase this article. Leonid Burakovsky, a, and Dean L. Prestona, Los Alamos National Laboratory, Los Alamos, NM 87545, USA Available online 21 August 2006. Abstract The Guinan-Steinberg (GS) formula for the shear modulus at all pressures is widely used in material strength studies. As we demonstrate here, the GS formula predicts a value for the shear modulus that is higher than its actual value at low to moderate compressions, even if it has the correct ultrahigh pressure limit. We show that the reason for this shortcoming is insufficient negative curvature in the GS shear modulus as a function of pressure, and propose a generalized GS formula which corrects this inaccuracy. Both the (standard) GS formula and new generalized formula are compared to the experimental data and ab initio calculations on the shear moduli of gold, aluminum, cobalt and beryllium. While the standard formula fails, the generalized one is in good agreement with data in each of the four cases. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Bavaro Sent: Wednesday, August 24, 2011 4:58 PM To: [log in to unmask] Subject: [TN] Gull Wing Lead - no heel fillet Hypothetical situation: Gull wing lead, land pattern error, zero heel (also zero toe) fillet. Hardware would not meet Class 3 workmanship requirements. An equation is being used to decide if the pad to gull wing lead lap solder joint is adequate to survive the intended thermal cycling environment. This would have been a question for Werner but I am sure there are others here who can shed some light on this for me. I know that part of the justification for why we have set our IPC standards where they are is partly based on years of testing. How could a mathematical calculation such as "Steinberg equation" justify a lack of Class 3 gull wing lead heel fillet? Any help is appreciated. ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. 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