Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

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SMT electronics assembly manufacturing forum.


Lead Free Process

Robert Sykoh

#7006

Lead Free Process | 21 June, 2001

Hi,

I am looking into lead free process. Do anybody has experience?? The composition used in SMT & wave.

Besides, what are the capital investment required??

Any advice is most welcomed.

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Robert Sykoh

#7007

Lead Free Process | 21 June, 2001

Hi,

I am looking into lead free process. Do anybody has experience?? The composition used in SMT & wave. I heard Sn,Ag,Cu & Sn,Ag,Cu,Bi. What are the major differences and concerns.

Besides, what are the capital investment required??

Any advice is most welcomed.

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CAL

#7014

Lead Free Process | 21 June, 2001

The data for this is overwhelming. My best advice would be to contact our lead-free specialists Lee Whitemann or Blaine Partee. Blaine's email is bpartee@aciusa.org Phone 610-362-1200 x 209.

Lee's email is lwhitemann@aciusa.org Phone 610-362-1200 x 208.

These two guys can provide you with majority of the data points you may have.

Also down load our tech publication at http://www.empf.org under the EMPFASIS Icon, the months you need would be Nov, Aug, Feb of 2000.

Enjoy

Caldon W. Driscoll ACI USA 610-362-1200 cdriscoll@aciusa.org

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Steve Brown

#7015

Lead Free Process | 21 June, 2001

I used to assembly 0402 devices on to a double sided PCBA using a 96% tin 4% silver alloy. This material printed fine but the higher processing temperatures did present a problem. This material had a melting point of 221 deg C which required a peak reflow temp of around 254 deg C. This obviously is well above the recommended temperature for an FR4 PCB. Basically the goal of the reflow profile was to warm up the board and the flux as with a standard eutectic paste and then try to minimise the time between melting to peak to solidification. This had a tremendous impact on our choice of oven, our requirement was for an oven which could maintain a zone temperature difference of 100 deg C between adjacent zones. And it needed and good cooling process. We were probably not treating the PCBA in the best possible manner but we found no problems with failures during lifetime testing.

Steve.

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ianchan

#7089

Lead Free Process | 26 June, 2001

I second that juicy bit from brownsj, Sn96/Ag4 process is what we are using too, currently for BIB runs, dunno about current capital investments needs, coz from what I understand, our company's BIB pioneer guy, personally designed the machines in current use, and asked general hardware-mechanic (read as Precision Tools) shop to assembly the machine bits together, mayhaps you can do the same?

quick calculations, do show that equipment self-design + self-made, instead of buying from the industrial mfg-vendors, can yield as much as 60% discount in setup costs$$$... (plus no such thing as ship & handling clauses for outside the USA)

then again, you have to know what u r doin, coz there's no warranty for either design specs. or assembly...hmmm.....

Good' Luck mate in your "adventure", should you choose the harder (dare I say more derived degree of professional satisfaction??) path, I did and darn glad I did :)

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monkey

#7185

Lead Free Process | 6 July, 2001

I have been researching lead-free paste for a while now and I will share with you what I can.

Firstly, SnAgCu seems to be the common industry choice. It really depends on your application - the cell phone/pda sector is primarly using different combinations of SnAgCu. Selecting your composition is the difficult part - there are so many patents out there that you have to be very careful what you use. My advice: choose 3 or 4 well known suppliers and see what they are recommending. The most economical way to buy lead-free paste is to find a company that has "off the shelf" products (mass produced) rather than getting a custom formulation.

Most alloys in the SnAgCu family melt around 217 degrees. (typical Sn63/Pb37 is 183) You need to do some research first. Find out what the capacity of your oven is. You will be looking at increased energy costs with the increased reflow temperature. Your peak temperature will be hovering around 260 + degrees with lead free pastes. Most newer ovens are capable of reaching such temperatures, but older ovens are not. Next, you will need to find out the specs. of your componenets. Many components are heat sensitive and will not tolerate the increased heat. Even though they may look alright on the surface, the internal circutry may be damaged.

As far as cost for the paste. You will find that you are paying more per jar, but due to the paste density difference, you will acutally be using a smaller amount of paste/joint. As far as the cost of the paste goes, it should be about the same as what you are paying now even though the cost of the jar is more.

There is some contriversity about the use of Nitrogen. Nitrogen is highly recommended to improve joint strength and appearance. But some companies have had success reflowing lead-free paste in air. If you are already using Nitrogen, then this is not an issue. If you are not using Nitrogen, it is a cost consideration. If you do not want the added cost of Nitrogen, talk to your paste suppliers and see what they recommend.

The alloy SnAgCuBi has also been recommended, but there are good points and bad points to this alloy. The Bismuth lowers the melting temperature about 5 degrees, and it has been shown to provide excellent joint strength and fatigue properties. The lower temperature can also eradicate fillet lifting. The problem with Bismuth is that it is completely incompatable with Pb. If there is any lead on the component terminations, pcb, etc., the quality of the joint is very weak and unreliable. The component industry isn't as far ahead with regards to lead-free products as the pcb and paste industry. Chances are that you will have to purchase some componenets that have Pb in the component terminations. Also, SnAgCuBi is hard to manufacture in a wire form.

There is alot of information out there about lead-free. Some good sites to visit are: www.leadfree.org (ipc website) http://www.nemi.org/PbFreePUBLIC/index.html (nemi website) www.pbfree.com

Also visit the webpages of different paste manufacturers (aim, alpha, loctite, indium, kester, etc.) and oven manufacturers (conceptronics, vitronics, heller, etc.)

Hope this helps! N

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