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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Silkscreen turns Purple

Views: 8643

#62653

Silkscreen turns Purple | 8 September, 2010

Hi, ran across a batch of PCB that has white silkscreen during receiving but turns purple/pink after our reflow process. SEM/EDX test can show there is no significant different element between the white and purple silkscreen. Can any help advice what did chemically happened during the process? Why is there a change in color after reflow?

reply »

#62661

Silkscreen turns Purple | 8 September, 2010

ENIG boards, correct? If so, you'll find that purplmation of your silkscreen has nothing to do with your process and everything to do with the quality of your in-bound boards.

reply »

#62662

Silkscreen turns Purple | 8 September, 2010

Hi Davef, ues, its ENIG. But do you know what the causes this? We send the board for testing but finds nothing defferent chemically between the white and the purple silkscreen. The supplier claim that its our process that is caused the changes.

reply »

#62663

Silkscreen turns Purple | 8 September, 2010

Technical data sheets from the ink supplier will: * Describe testing has been done * Recommend to their customers the limits of exposure to thermal, chemical, and mechanical conditions.

reply »

#62665

Silkscreen turns Purple | 9 September, 2010

We're guessing the ink wasn't fully cured, when they finished the ENIG.

If the supplier is correct that it was your 'process that is caused the changes,' then they certainly won't mind you bringing over a couple of unstuffed boards and running them through their oven in a simulated reflow profile, just to placate you. This doesn't require a fancy reflow oven that they probably don't have. A Blue-M baking oven will be just fine. They'll have one on those.

reply »

#62666

Silkscreen turns Purple | 9 September, 2010

I've seen the purple silkscreen before on ENIG board built with PbSn process. I would think that if temp is the issue the lower process temp would not have caused the purple ink. I remember that the flux I used was water soluble and I attributed the discoloration to additives the boards were exposed to during the wash cycle.

I experienced the purple silkscreen on more then one batch of boards. My customer noticed but didn't complain. There weren't any quality issues with the boards as a result of this.

reply »

#62708

Silkscreen turns Purple | 15 September, 2010

We drilled a hole in the centre of the LGA and put the thermocouple inside, so we measure the exact temperature between PCB and device. http://www.jewellerybeadsale.com/

reply »

#62709

Silkscreen turns Purple | 16 September, 2010

Hi All, thanks for your precious reply. We had been trying very hard to ocnvince the customer that there is nothing wrong with the PCB but they are still unwilling to accept the change of silkscreen color. We attribute the silkscreen issue to a bad batch of ink. So far, there is no headway to the case, new batches of PCB does not show this issue, no process change were made both on our side as well as the supplier's.

reply »

#62727

Silkscreen turns Purple | 17 September, 2010

All,

Get the material data sheets, lot numbers of ink, supplier's process flow, bare boards with ink lot applied ( qty 20), Contact the ink supplier and perform a 3company DOE.

reply »

3D SPI

ii-feed SMD Intelligent Feeder