A. J'espère que ce qui suit sera utile:
Of course we have a spec, but I can't give you that. It can look like this
(al wedge in this case):
1. Copper according to xxxx, thickness xxxx, microhardness xxxx, structure
according to xxx, flatness xxx, etc
2. Nickel adhesion layer according to xxx,
3. Nickel plating according to xxx, thickness xxx, microhardnes xxx, grain
structure according to xxx, Ni %, P%, organics maximum ppm, asperity Ra,
voids maximum xxx, bath type xxx (must not be changed without permission),
friction coefficient xx, etc
4.
5. Gold according to xxxx, thickness xxx, etc
6. Shall meet following environmental tests: (not of interest in bonding
point of view)
7. Before shipping, shall meet bond test with xxx wire, thickness, hardness,
bond type, maximum bond failures accepted xxxx, sample number according to
xxx etc
8. Visual requirements: shall meet our specification xxxx
9. Each delivery shall have n test coupons with accepted solderings and
bondings according to our spec xxx
I have given you, as well as Trikeman, a reasonable platform to stand on,
but you have to do some homework yourself, can't just copy our company
bonding profiles, no guarantee it would work in your case.
You may study the below (very good) example
http://www.desy.de/~alberto/bond_specs/bondweb.html
Hope I have not made you too disappointed, brother.
Inge
----- Original Message -----
From: "Creswick, Steven" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, March 21, 2007 3:13 PM
Subject: Re: [TN] Gold Ball Bond attaching surface roughness
Arnaud [Victor],
Personally, I do not get all hung up on the surface finish of the plating
[unless it is outlandishly rough] - it is the QUALITY and CONSISTENCY of the
plating that is of paramount importance to me in bonding. [In many cases,
the apparent surface finish of the plated film will accurately reflect the
underlying surface finish of the base part, so that is the element which
needs to be controlled - not necessarily the surface finish of the plated
film. Use Ingemar's suggestion for the suggested surface finish of the base
metal part].
A good plater will have ways to monitor bath quality and resulting thickness
[if you agree on where to take the thickness measurement]. I do not recall
seeing any surface finish measurement equipment at a plater [having said
that I will surely get blasted by those that do/have :-) ].
I have not found a wire bonder [equipment manufacturer] which specifies the
characteristics of the surfaces their bonders will function on. There may
be generics on the type/s of plating and [maybe] basic thicknesses - but
typically this is gleaned from what they see their customers using, and not
an in-depth knowledge of reliability on the equipment manufacturers part.
They want to sell [reliable and consistently functioning] equipment. It is
our job to make it construct reliable bonds.
Yes, it is greatly important to standardize everything and NOT be playing
with the equipment settings on a daily/weekly basis. Somewhere along the
line, one must qualify the bond schedule for the product and I believe that
to be OUR job, not the equipment manufacturer. We will be the party
ultimately held responsible for failure.
If aluminum bonding, I would be careful not to have more than a flash of
gold, say 2-5 µinches - am concerned about thickness, not surface finish.
With aluminum bonding, we are bonding through the gold, so in reality the
gold does not have to be of the greatest purity [this is in direct contrast
to thermosonic gold ball bonding for example where we ARE bonding to the
gold].
I don't develop the bond schedule based on surface finish as much as I do on
the characteristics - purity/softness, thickness, etc. of the plated film.
Hope I did not muddy the water too much further.
Steve
-----Original Message-----
From: arnaud grivon [mailto:[log in to unmask]]
Sent: Wednesday, March 21, 2007 7:36 AM
To: TechNet E-Mail Forum; Creswick, Steven
Subject: Re: [TN] Gold Ball Bond attaching surface roughness
Hello,
Although my current interest is more on Al wedge wire bonding (I made a
post on that), I take the opportunity to comment on this one. I just
can't imagine that bonders do not have specifications about the NiAu
plating the bonds will have to adhere.
Normally as soon as large volumes are at stake, everything needs to be
standardized to have the less adjustments.
Are we saying that the wire bonding is always adjusted according to the
incoming finish?
Best regards,
A. Grivon
Creswick, Steven a écrit :
> 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,
>
>
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