Our subcontractor would like that gold! What's the price per kilograms? What are the delivery terms? Yum-yum-yum.. Inge ----- Original Message ----- From: "Creswick, Steven" <[log in to unmask]> To: <[log in to unmask]> Sent: Monday, March 19, 2007 6:02 PM Subject: Re: [TN] Gold Ball Bond attaching surface roughness Victor, If I found the correct pictures on Steve's web site - Ball bond 1, 2, and 3, [upper right side of page 1] you do have a somewhat rough surface to bond to. You are unlikely to find someone that can give you a specific surface finish requirement which is equivalent to a given degree of reliability. Just as Ingemar says, there are many variables coming in to play - bond schedule, plating quality/hardness, cleanliness, clamping, tool style, etc. Very rough surfaces can be bonded quite well - aka some thick film [cermet] golds [spoiled by in-house golds which were essentially glass-free at the surface, whereas many others required burnishing]. I believe this to be because of their 'soft' nature. Whereas, a mirror-smooth, plated cobalt-doped, edge connector gold is virtually impossible to gold ball bond to simply because it is so very hard. The point being made is that just looking at surface finish without taking into account the plating is meaningless. Your substrate, the copper, is basically 'hard' when compared to the pure gold ball. If your bond schedule is on the lite-side [and the plating is bondable], you will bond to the peaks only. You may get decent pulls, but you will generally not fully involve the full underside of the ball bond. To an extent, you can increase your bond energy by either cranking up the temp, time, and/or power and get more deformation of the ball bond. You will likely involve more than just the peaks, but to what extent can only be judged by doing wire pulls and accelerated aging. Then you can do what some folks do and crank up the bond force and smash the bejeebers out of the bond without necessarily improving the reliability of the bond - but it certainly is smashed into the substrate! The more energy I toss in at this point, the greater the opportunity for weakening the bond in the region directly above the ball. This is what I would call a first bond neck/heel break. There is a heat affected zone in the wire immediately above the freshly formed free air ball, as a consequence of the flame-off step of the bond sequence. Just because I get a neck break at this point during wire pull [meaning the ball stuck] does not give me the warm fuzzies. It just means the neck was weaker than the ball bond ... what did it fail at magnitude wise?? Plating can really play a big roll in apparent surface finish. From the pictures, it does not look like gold. Are you bonding to silver? Did you say what your plating scheme was?? A nice nickel barrier plate followed by a [soft] silver plate should hide many of the asperities of the underlying copper .... As Ingemar says, you could always go in and coin the bottoms of your divots before [or after] plating to help improve the surface finish. Alternatively, if you have equipment which can put down a gold bump into the divot, then you could place your ball up on the chip and the second bond down on your bump. I find that getting balls to bond to difficult surfaces is generally much easier than getting the second bonds to stick in the same place. In conclusion, your surface is not as rough as it potentially could be. A great deal is going to depend on your plating scheme. I can't give you a generic number to use for surface finish, but common wisdom is that the rougher the surface, the more likely you are to have bond failure. Steve -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar Sent: Monday, March 19, 2007 11:40 AM To: [log in to unmask] Subject: Re: [TN] Gold Ball Bond attaching surface roughness The matters you speek of were handled decades ago. Try to find any of these : - J.m. Vandenberg, R.A. Hamm, A continous X-ray study of the interfacial Reactions in Gold-Aluminum Thinfilm Couples. J.Vac.Sci. Tech 19 (1981) 84-88 - E.Philofsky, Intermetallic Formations in Gold-Aluminium Systems, Solid-State Electronics 13 (1970) 1391-1399 - G.Majni, C.Nobili, G.Ottaviani, M.Costato, E.Galli, Gold-Aluminium Interactions and Compound Formations, J.Appl.Physics 52 (1981) 4047-4054 -B. Lan, S. Pinamaneni, Thermosonic Gold-Wire Bonding to Precious-Metal-Free Copper, Proc. 38th Electronic Components Conf.(IEEE) L.A. Cal. 1988, 546-551 -J.Falk, J.Hauke, G.Kyska, Wirebonding on PWB, Circuit World 20 (1994) 8-13 -K.Toyozawa, K. Fukita, S.Minamide, T.Maeda, Development of Copper Wire Bonding application Technology, IEEE Trans.on Components, Hybrids and Manuf. Technology CHMT-13 (1990) 667-672 These are what I can give you, I have many more references, but I have no time to dig just now....maybe later. If you have good luck, George Harman may read these lines, and give you exact answer at once. I have performed studies of the nano/micro-welds that take place after thermosonic ball bonding, and if we speak in very general terms, the asperity ought to be in the range 0.1 - 0.5 micrometers, much depending on the microhardness of the parties. These small bonds take place at temperatures as high as 2,000 Centigrades during milliseconds, and the general experience is, that most important of all parameters are these: cleanliness (lubricant free), matching microhardness, matching ultrasonics. The surface roughness may come as number four or five, I don't know. Furthermore, if the surface isn't smooth enough, you can place a special tool on the horn instead of the capillary or wedge, and "polish" by means of the ultrasonic and the pressure. As I said, Trikeman is more guru at this, 125 years at CTS must exist still in his organic computer. Good Luck Inge -----Original Message----- From: [log in to unmask] [mailto:[log in to unmask]] Sent: den 19 mars 2007 15:40 To: [log in to unmask]; Hernefjord Ingemar Subject: RE: [TN] Gold Ball Bond attaching surface roughness Inge, Thanks for sharing the HCC document with me. Very interesting article. My main concern is to find out guidelines for ball bond surface roughness to ensure adequate IMC formation. Victor, -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar Sent: Monday, March 19, 2007 9:08 AM To: [log in to unmask] Subject: Re: [TN] Gold Ball Bond attaching surface roughness HCC are great too, they really know how to define nailheads etc. Inge http://www.hccindustries.com/files/HCC-Package-Design-Guide.pdf -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Creswick, Steven Sent: den 19 mars 2007 11:21 To: [log in to unmask] Subject: Re: [TN] Gold Ball Bond attaching surface roughness Ingemar, I agree with your pin oscillation caution statement! Might I ask if your plater is local or outside, of the country? Am assuming Electroless on your pins. Correct? Alas, grounded for another weekend. Fear not. Will not drop! Steve -----Original Message----- From: Inge [mailto:[log in to unmask]] Sent: Friday, March 16, 2007 3:02 PM To: TechNet E-Mail Forum; Creswick, Steven Subject: Re: [TN] Gold Ball Bond attaching surface roughness Both, in fact. Yep, the plater cooperates understandingly. Nota bene: if you bond on nailheads or any similar pins, you need keep an eye on the U/S frequency. The pins can swing with the horn, and that can cause poor adhesion. So, Trikeman, you begin to feel altitude excitement. I understand. I've seen young bird's whole body vibrate and suddenly they can't resist any longer, but jump from the bird nest and swing up in the sky, anxiously but triumphing. Go, Trikeman, fly with the eagles! But don't drop things on my head. (I don't know how much bird you become up there) Inge ----- Original Message ----- From: "Creswick, Steven" <[log in to unmask]> To: <[log in to unmask]> Sent: Friday, March 16, 2007 11:12 AM Subject: Re: [TN] Gold Ball Bond attaching surface roughness Okay Ingemar, Are you putting the ball on the [nail head?] pin, or the wedge? I bet your plating/plater has a lot to do with your success :-) Sometimes you crack me up! I need the weather to calm down so I can go flying. Starting to grow roots have been on the ground so long. Finally loosing enough snow that I might be able to get out on the field. Steve -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Sent: Thursday, March 15, 2007 5:18 PM To: [log in to unmask] Subject: Re: [TN] Gold Ball Bond attaching surface roughness Copper Cup...when is that? Sorry, I know you are not to play with until on Friday. Even if the surface you are looking at may seem rough in a macro-looking perspective, the micro ditto may serve well for the ball or wedge. Hence, we do bonding on rough glass feed-true pins, which are absolutely not thought for bonding, but it works fine. Try! And do pull test! Inge ----- Original Message ----- From: <[log in to unmask]> To: <[log in to unmask]>; <[log in to unmask]> Sent: Thursday, March 15, 2007 7:48 PM Subject: RE: [TN] Gold Ball Bond attaching surface roughness The application I am referring to is a device where the ball bond, BCC, is placed on a copper cup which also serves as the solder fillet to the PWB pad. This cup is really rough exhibiting tooth like structure similar to those of the vendor treated side on copper foil. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Sent: Thursday, March 15, 2007 12:23 PM To: [log in to unmask] Subject: Re: [TN] Gold Ball Bond attaching surface roughness Agree with Trikeman, the semi process is a epitaxial process using "refractory" metal, and the asperity is not measureable on normal tallysurfers, i.e. <0.1 um. Only situation may be with semi chips with plated bond pads, but then we talk gold. And these have never caused us any problems either. You needn't bother. /Inge ----- Original Message ----- From: "Creswick, Steven" <[log in to unmask]> To: <[log in to unmask]> Sent: Thursday, March 15, 2007 1:36 PM Subject: Re: [TN] Gold Ball Bond attaching surface roughness Victor, Sorry, don't have a number to give you. We do it all day long ... and the IC mfr's know how to make the bond pads.... Typically smoother is better, but if one were to look at the plating on a lead frame at high enough magnification, it is certainly not smooth either. Possibly someone has some form of spec on the surface finish of a bond pad. All that I am aware of is pad thickness. If no one has a surface finish number, I might be able to run some next week. Steve C -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor G. Hernandez Sent: Thursday, March 15, 2007 8:25 AM To: [log in to unmask] Subject: [TN] Gold Ball Bond attaching surface roughness Fellow TechNetters: Typically I have observed ball bond attached the alunium window of a chip, and copper lead frame. Are there any criteria for the roughness of this surface for establishing a good intermetallic formation? Victor, THE INFORMATION CONTAINED IN THIS E-MAIL MESSAGE AND ANY ATTACHMENTS SENT FROM GENTEX CORPORATION IS GENTEX CONFIDENTIAL INFORMATION INTENDED ONLY FOR THE PERSONAL USE OF THE INDIVIDUAL OR ENTITY NAMED ABOVE. If you are not the intended recipient, you are hereby notified that any review, distribution, or copying of this communication is strictly prohibited. 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