Letter 39011

What's "thick Au" ? [China] 

January 12, 2006

In FPC(Flexible Printed Circuit) field, I often hear the word "Thick Au", but I can't find any information about it, and what I know "Thick Au" commonly is above 0.5 micron thickness. So we need a special bath to prepare so thick film by plating! Can you Suggest to me some baths?

For all Above
1.what's "Thick Au",Is there any standard to define the word
2.how can i get Au film above 0.5micron in 30 second? Can you suggest to me some baths?

Yang
- ShenZhen, China

I don't think there is such a standard as "thick Au". The term itself is very vague. Gold plating is priced on a specified plating thickness per square ft. and market value. If your customer is using this term ask them what the minimum thickness that is required. Generally for printed circuits it's between 40-50 microinches, I forget the exact minimum. As far as acheiving 0.5 micron Au plating thickness in 30 seconds, forget it. Hard acid golds are only about 45% current efficient. I know when I plated PC boards it took me 12 minutes to get a thickness of 45 microinches, plating at 7 asf with Au concentration at 0.85 tr.oz/gal. The only gold that would plate as fast as you described, would be a Au bath with free cyanide and higher Au concentration, but dry film photoresists and other common coatings would break down right away. Gold concentrations are usually 1 tr.oz/gal for rack plating, plate @ 5-10 asf, if all other bath conditions are right you should get 40-50 microinches in about 10 minutes. Good luck!

Mark Baker
Process Engineer - Syracuse, NY, USA

Hi, Yang
Thick Au means thicker thickness of gold if you want higher thickness you have to increase gold concentration in the bath. let me know which bath you using SOFT GOLD, HARD GOLD.

Milind Patel
- Toronto, ON, Canada

Dear Yang,
1.Thick 'Au' means Thick Gold ( Au is the short form from the Latin word of Aurum (gold)).The periodic table represents short forms for all metals and most of them are derived from Latin).Another eg; Sodium is Natrium (Na)in Latin.
2.To get 0.5 Micron in 30 seconds:Please contact your supplier. They will be able to Guide you.

I can give you some basic calculations.

178 mg gold on one square decimeter plated is 1 micron.
Diffrent plating solutions will give various plating speed from 1 ampere per DM2 for one minute will deposit from 20 mg of gold to 110 mg of gold depending up on the formulations.

First understand your plating bath and its speed of deposition and calculate the current and the time.

Now coming back to your requirement of getting 0.5 Microns in 30 seconds,please remember PCBs are plated with hard gold and the efficiancy is usually within the range of 40-60 mg per amp minute.
Let us take the bath speed as 60mg/amp minute.
U will get 1 micron in 3 amp.minute per DM2.
i.e:1 amp for 1 minute/DM2 = 60 mg
3 amp for 1 minute/DM2 = 3 x 60=180 mg=approx 1 micron
3 amp for 30 secs/DM2 =180/2= 90 mg = 0.5 Micron
But make sure your gold bath can carry 3 amps current per DM2.
Hope u are clear.

Regards

T.K. Mohan     plating process supplier  Mumbai, India

Ted,

It takes so much of time to answer thease kind of questions.(calculations involved).And no responses about what they do afterwords to deal with their problems!

T.K. Mohan     plating process supplier Mumbai, India

Yes, it's a sign of the times that many people don't send proper "thank-you notes", TK. But our aunts who nagged us to do so and explained how the notes should be worded have passed away :-)

finishing.com does what we can, such as writing privately to people who post repeated questions without acknowedging the posted answers, requiring that people describe their real world situation rather than post abstract questions, directing people to books if the answers are too long and complicated for an internet posting. But we can't always tell how involved an answer will be, and sometimes even poorly asked questions inspire an educational dialog.

But don't feel obligated to answer every question; if a question remains unanswered it usually reflects poorly on the way the question was asked.

Ted Mooney, P.E.  finishing.com Brick, NJ

Ted is correct that thank you notes are a thing of the past. I view the field of electroplating and finishing very challenging and rewarding. I don't think many of us that are willing to share our knowledge and experience really expect a thank you note. What would be nice to see is how these suggestions resulted in positive, and yes, even negative results. It would enhance the educational perspective of finishers world wide. So let us know how you are doing, it will benefit everyone!

Mark Baker
Process Engineer - Syracuse, NY, USA

Dear all
Nice to see Baker's response. I do not think that any body expects a thank u letter. So many people give practically and technically approved suggestions(otherwise it will not pass thru Ted's screening)that they expect whether the person is convinced or doubtful. If he/she responds,it can create an atmosphere to have more experienced people join to share their views and he/cancan benefit from the discussions.
That is all what I meant.
Regards.

T.K. Mohan     plating process supplier Mumbai, India

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