Ioan,
If you are trying to use ACF to fix a connector to a rigid board,
surface finish is the least of your worries. I presume you are referring
to a heat curable acrylic adhesive filled with metal coated plastic spheres?
You will have to hold co planarity between the board and the connector
contacts to something like 20 microns to get a reasonable chance of
contact with all the fingers. Even then as you will be crushing the 30
micron diameter balls (I think that is about their diameter) by anywhere
between 0 and 20 microns. This will compromise the reliability of the joint.
I'd strongly recommend talking to both the adhesive manufacturer and the
bonding machine manufacturer. They may be able to help.
FYI, we've used ACF for bonding flex parts to components with flat
substrates. Both used Enig pads and passed consumer level reliability quals.
Good luck.
Thayer, Wayne wrote:
> Hi Kim!
>
> Sorry, but I think I've given you almost all I know on the subject. Haven't used them myself because I've always managed to solve the problem other ways. If we are compressing spheres, then it stands to reason that the force vs. displacement will be parabolic, as you say, although displacing the resin will enter into the equation too.
>
> Wayne
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Haynes, Kim
> Sent: Monday, March 10, 2008 12:14 PM
> To: [log in to unmask]
> Subject: Re: [TN] Bonding on ENIG - correction
>
> Morning Wayne,
>
> How is the compression ratio controlled during the ACF process? Do you know if the ACF material has a parabolic curve for compression vesus resistance similar to the elastomer (MAF) socket mats? I have had a very difficult time using elastomer sockets because of this curve and the fact that the distance from too loose to too tight is very small.
>
> Thanks,
> Kim Haynes
> Interface and Clock Products
> High-Speed Serial Link Applications
> Texas Instruments, Inc.
> 214-567-2057 Telephone
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne
> Sent: Monday, March 10, 2008 10:36 AM
> To: [log in to unmask]
> Subject: Re: [TN] Bonding on ENIG - correction
>
> Oh boy! That's much more "fun"!
>
> ACF relies on conductively coated elastomeric particles for conduction. Key to using them is the usable compression ratio: Calculate the sum of the probability distributions of the planarity errors of the two materials being bonded together and make sure the ACF can handle that range (obviously only the relative planarity of the pads is important--not the dielectric between the pads!). Problem is that to bond very tiny pads with ACF you need very tiny conductive particles. This in turn implies higher co-planarity requirements for the surfaces. I have heard that vendors are working on nano-tube type structures to assist with this problem by making the useful compression ratio very large, but I haven't seen anything on the marketplace.
>
> As far as plating finish goes, I would still want more than 30nm! With that thin of a coating, I would expect Ni coming through. With a "more normal" ENIG Au thickness of 150-200nm you are probably OK. Personally I prefer electroplated Ni and Au since the possibility of the dreaded "black pad" is far reduced. I would still think you would want to minimize the Cu thickness just because thicker material is likely to have more planarity issues.
>
> Wayne
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
> Sent: Monday, March 10, 2008 8:54 AM
> To: [log in to unmask]
> Subject: [TN] Bonding on ENIG - correction
>
> Inge, Wayne,
>
>
>
> Thanks for the replies!
>
>
>
> There is a correction I have to make and I hope you will forgive me, but I am a complete layman when it comes to bonding.
>
>
>
> We are talking about ACF bonding... How will this affect the surface finishing?
>
>
>
> Thank you,
>
>
>
> Ioan
>
>
>
> ________________________________
>
> De : Ioan Tempea
> Envoyé : 7 mars 2008 08:06
> À : 'TechNet E-Mail Forum'
> Objet : Bonding on ENIG
>
>
>
> Hi Technos,
>
>
>
> A connector has to be bonded on 2 mil wide traces. Is ENIG suited as a surface finish for bonding? If yes, why, if not, why and if it depends, why?
>
>
>
> Or otherwise said, I have a PCB that will get some SMT parts on both sides and then a couple hundred golden fingers will see bonding. I was presented with 2 options for the PCB finish:
>
> a) Immersion Gold : 0.03um Au over 3um Ni over 25±10um Cu
>
> b) ElectroBonding Gold: 0.3um Au over 3um Ni over 25±10um Cu
>
>
>
> Which one is to prefer?
>
>
>
> Thank you,
>
>
>
> Ioan
>
>
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--
Eric Christison Msc
Mechanical Engineer
Consumer & Micro group
Imaging Division
STMicroelectronics (R&D) Ltd
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