FAB instruction for ROHS Boards

[shenthil]

Hello,

As a PCB Layout Engineer, Is there any FAB instruction (for ROHS Boards) that we need to give in FAB drawing or Gerber for Manufacturer?

or

In FAB Drawing(Gerber), What are the instruction do we need to give for ROHS Boards?

Thanks and Regards
Shenthil

[Bhagyamala]

Hi,

For RoHS board fabriation we want to give some specifications.

Type of Surface Finish

Board material which suits the Rohs compliance

[Carl_at_xrite]

Most pcb materials (FR4) are already RoHs compliant regardless of the Halides contained in them, The halides are what gives you your flammability rating (94v-0)

You want a High temp laminate with a high decomposition temperature, high Tg and Low CTE due to the elevated temperatures at the assembly level especially for multi-layer applications.
Also depending on your application you want to watch your moisture absorption spec. as the trend would be the higher the decomposition temperature the higher the moisture absorption percentage, this could present a problem when using High gain analog front ends.

As far as the surface finish you have multitudes of options
1. immersion silver- great solderability but requires alot of handling and storage specifics is very cost effective in comparison to HASL. widely available

2.Immersion gold(ENIG), good shelf life and solderability, has some problems like black pad which result in poor solderability a bit more expensive, very flat surface
2-5 microinches of gold over @120 microinches of nickel (this is my choice) widely available

3. Immersion tin- work with your vendor on thickness depending on your process, shelf life is somewhat limited baths are hard to maintain and if your process includes many heat cycles you might see a copper migration resulting in poor solderability. very flat surface somewhat available

4. Sn,Ag,Cu (relatively new) a new "HASL" dip process I haven't seen many houses utilizing this yet but I would suspect that soldering to a surface using the same elements as your solder may solder pretty well , Don't know much about the shelf life, I could see contamination issues in maintaining the solder bath chemistry that could result in solderability issues. I would wait for industry response and IPC recommendations before adopting this as a finish availability is somewhat limited

5. O.S.P. flat over bare copper, limited reworkability and shelf life, requires specific handling requirements, widley available

One thing you want to note is that you want your fabricated PC board to be fabricated and processed in accordance with the RoHs initiative, you don''t want a RoHs board being washed in the same rinse as a board that was done in HASL.

We spent a lot of time evaluating finishes laminates as well as our process and solderability over the last 2+years in preparation for this.

Hope you can use some of this information