Direct Metallization on ABS
An ongoing discussion from 1996 through 2014 and counting . . .(1996)
Q. Does anybody hear any news about direct metallization on ABS and ABS/blended polymer ? How does it compare with conventional plating on plastics ?
Best Regards,Ricks W. Lambert
A. Ricks, What does that term "direct metallization" mean to you? You can't plate plastics without some form of "metallization" onto the plastics before actual plating. We use silver nitrate to "metallize" the ABS before plating.
- Rhode Island
A. Dear Ricks,
About a year ago I've done a large process design project for electroless (autocatalytic) plating on ABS and some other plastics. Almost any "metallization" can be done after pretreatment. I found it to work the best coupled with plasma etch.
A. Ricks, I agree, you must describe what you mean by: "Direct Metallization." ABS is easily metallized via Electroless Ni after providing Pd nuclei via standard processes. Alternatively, you can Vapor Deposit a Ni thin film then coat with E'less Ni although adhesion is not as good as the Pd route.
TUTORIAL FOR NEWBIES (2014): "Direct Metallization"
A. Dear Ricks,
There is a new system on the market for plating directly on ABS and ABS-PC substrates. The difference to conventional plating technologies is that this process does not require any electroless metallization (e.g., copper or nickel). The first metal layer is directly plated acid copper. The ABS substrates are treated to achieve an electrical conductivity on the surface. This conductivity is good enough to start directly with electroplating of copper.
Best regardsStephan Hempelmann
A. Ricks & fellow tank jockeys:
I have recently undergone a baptism by fire on all current direct metallization processes. Here is what I have learned: Direct metallization was developed for the printed circuit industry as an alternative to E'less Copper to get rid of the "allegedly" toxic formaldehyde used as the reducing agent in E'less Cu. Direct Metallization ("DM" from now on) is used to metallize through-holes and blind vias so that a conductor is present on the thru-hole ("TH") surface and now the TH can be electroplated with normal current-driven plating processes. Electroless Cu was used previously for this step. It is still widely in use in many shops as there are pitfalls in the usage of the various DM processes which must be balanced from a production point of view against the usage of the more robust Electroless Cu from the environmental point of view.
DM process GENERALLY fall into two classes: 1. Those that deposit Carbon as the conductor onto the non-conductor that you wish to render conductive, and 2. those that deposit metals. Of the metal depositing process, Palladium is the favorite. Some deposit it as finely dispersed pure palladium clusters, and others deposit it from colloidal forms. One process subsequently converts deposited Pd into the semiconductor PdS, while others build "mounds" of Pd, while still others build interconnected Pd cluster networks. Common to all processes is that when exposing your workpiece to the DM, the conductors and non conductors alike get DM. Then expose the workpiece to an etchant to back etch the conductors through the DM layer to remove the DM from the metallic conductors while leaving the DM on the nonconductors. This enhances bond strength of subsequently electroplated layers to the Cu or whatever conductors are used. The DM layer on the non-conductors remains since there is no conductor underneath it being attacked by the etchant. Then electroplate. Works great every time.
DM processes GENERALLY have the following properties: 1. Carbon DM: Adhesion is poor, but process control is unreasonably simple. Seriously. Just pour it then walk away. Come back in a few months and pour some more. 2. Pd DM: Adhesion can approach that of E'less Cu, but process control is complex and involved. They are both expensive. And they are both messy.
With regards to ABS etc, all DM will work but ABS has a long successful history of metallization by standard Sn/Pd. Only reason to change is to get rid of the chromic acid etch step, but it will still required on all DM processes if you want to maintain adhesion strengths (although vendors may deny this).
Hope this (late) info helps out. Contact me for details if you are still interested.
A. Dave gave a comprehensive explanation on DM. It works fine for PCB and ABS. On ABS blends and on geometrically complicated parts there are some difficulties so Pb/Sn is still the most reliable process.
chemical process supplier
February 18, 2009
A. According to my experience, the two methods David K. mentioned are usually used in PCB (Printed circuit board), for the through hole metallization. Actually, conductive polymer is also widely used for the direct metallization for PCB.
For David G: how can you use silver nitrate to "metallize" the ABS before plating? How to conduct?Kevin Zhu
- Shenzhen, Guangdong Province, China
Hi Kevin. David G. is referring to something like the Brashear process, similar to how mirrors are made: a two-gun system applies silver nitrate and a reducing agent to deposit a thin film of conductive silver metal. This process was very widely used in vinyl record manufacturing to metallize the lacquer master. To my knowledge it has no applicability to printed circuit boards though.
TUTORIAL FOR NEWBIES: "Electroless" vs. "Copper Replacement"
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Can't fill 20-25 µm Plated Thru Hole(2006)
Q. I am a process engineer of copper plating line and we are currently encountering voids on filling the Plating Through Hole (PTH) with 25 um top diameter and 20 um bottom diameter with 50 um thickness of Polyimide (PI). The material to be plated is 4 um Cu / 50 um PI / 4 um Cu in terms of thickness. We have metallization process prior electrolytic copper plating. The machine we are using for Copper plating is vertical plating and we have separate control on the current for the left and right side. We have tried using a low current density to slowly fill the PTH but still voids is encountered.We have also tried closing the small diameter first by applying current on small diameter side only using low current density and then reversing te orientation on the bigger diameter side still using low current density but still voids were encountered. Since this product is new to us and I am also new in copper plating , Can anyone help me on how to fill this PTH with copper without voids? Thanks a lot...Meredith Delfinado
Substrate Manufacturing - Philippines
Perhaps you could describe the exact voiding you are observing. Do you see interrupted plating down inside the via? For example incomplete sidewall coverage? Or does the entire via fail to plate? These may have different root cause. 25 micron diameter is a VERY unusually small dia. via in a 4/50/4 micron PI substrate. Are you just blasting right thru the metal & PI together with a YAG or Eximer? My first suspicion would be failure of the Direct Metal Process (or sputter) to properly cover the sidewalls. Direct Metal processes all have unique process windows that you need to determine by experiment for that very small via you are trying to process. And these DM processes RARELY operate at high yield at the manufacturer's recommended parameters. You need to find your own optimum. My second guess would be the photoresist or laser slag not well developed or cleaned out of the via prior to DM, and this presents a loose fragmented surface for the DM to deposit onto and as result the crevices present are problematic to the DM & Plating process.
Hope it helps, Pare
Update: What is the best metallization for ABS today?January 31, 2014
Q. I wanted to know the best metallization process for ABS plastics. Also its feasibility in today's world. And will the metallization process affect the properties of the plastic in any way?RAMEEZ MALIK
National Institute of Technology - ROURKELA, ODISHA, INDIA
A. Hi Rameez. Although this thread includes some old postings, I think it's still useful.
But there is no such thing as "best" or there would not be multiple approaches. If you mean what is the most robust process, I think automakers are still using the old traditional chromic-sulfuric etch, followed by Pd/Sn seeding, followed by electroless nickel plating before copper-nickel-chrome for exterior automotive parts.
Yes, the process affects the properties of the ABS, turning the surface spongy, followed by metallic ... but I think the ABS retains good mechanical properties. Good luck.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
February 3, 2014
Q. Thanks Ted. There is still one more question that I'd like you to answer. I have heard that plasma etching is a good metallization process for ABS plastic as it does not wear off with time. Do you have any idea regarding this? And since I will be experimenting on the plastic after metallizing it, changing of the properties is a concern.RAMEEZ MALIK [returning]
National Institute of Technology - Rourkela, Odisha, India
A. Hi Rameez. I was under the impression that "plasma etching" was an alternative to chromic-sulfuric etching to roughen the surface. Although a lot of plastic is vacuum metallized, even down to mylar party balloons, my understanding of vacuum processes is limited to book knowledge.
Still, as I say, for the most robust application, automotive exteriors, I don't think OEMs use vacuum processes in lieu of the palladium seeding and copper-nickel-chrome electroplating. And I do remember several messes the automotive industry got themselves into in their eternal lust to replace expensive copper-nickel-chrome electroplating with vacuum processes.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
April 4, 2014
The problem with plasma etching is that you do not get any polarity at the plastic surface.
Etching has two objectives:
1. To make the oxidation of butadiene
2. To make the surface hydrophilic, because the surface of plastic is hydrophobic.
Plasma etching does NOT make the plastic hydrophilic.
- Oradea, Romania
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