Gold Embrittlement

Gold Embrittlement Solution

What is the problem?

Gold has been a big part of electronics for many years, mainly due to the corrosion protection that gold offers. In the early days, layer of gold was applied as a thick layer and this led to problems with solder joint formation, the gold layer created an inter-metallic condition that could then create fractures in the solder joints.

Gold Embrittlement Example

Military/Aerospace and some levels of industrial standards would specify the removal of gold plating from components before they were to be soldered to the PCB to try and inhibit the formation of this gold inter-metallic and the higher percentage risk of fractures forming in the solder joint during end use, especially where the PCB’s were destined for harsh environments. When you also factor in the almost total market domination of ENIG (Electroless Nickel Immersion Gold) finish on PCB’s, the risk of soldering a gold component to a pad which, itself, is making a contribution (minimal, but still a contribution) to the gold percentage in the solder joints means a real potential for embrittlement caused by gold dendrite growth.

Some of the historic research into gold embrittlement would reference in specific thickness of the gold plating and for many years that stood as the J-STD recommendations for the way that many assemblers would process gold legged/padded components. But recently that has changed as it is now proven that gold dendrites inside solder joints can form no matter what the thickness of gold due, in part, to other factors.

The growth of the gold dendrites can occur when the solder quantity at joint formation is not enough to offer a complete dissolution or if the dwell (soak) time is not long enough. So, the many factors that are involved in the risk of gold embrittlement are –

Gold Thickness
Solder Type
Solder Quantity
Ramp rate and dwell times
Condition of gold layer

To eliminate the risk, the safest option is to remove the gold before assembly.

The change was reflected in the J-STD-001 from rev E to rev F –

J-STD-001 Revision “E” stated :

4.5.1 Gold Removal

Gold shall be removed:

a. From at least 95% of the surfaces to be soldered of the through-hole component leads with 2.54 μm [100 μin] or more of gold thickness.
b. From 95% of all surfaces to be soldered of surface mount components regardless of gold thickness.
c. From the surfaces to be soldered of solder terminals plated with 2.54 μm [100 μin] or more of gold thickness.

A double tinning process or dynamic solder wave may be used for gold removal prior to mounting the component on the assembly.

J STD-001 Revision “F” (For all classes) now states: (the changes are underlined)

4.5.1 Gold Removal

Gold removal is performed to reduce the risk of failure associated with embrittled solder. Gold embrittlement is not a visually inspectable anomaly. In cases where analysis has determined there is a gold embrittlement condition, the gold embrittlement shall be considered a defect, see IPC-HDBK-001 or IPC-AJ-820 handbook for guidance. Except as noted above, gold shall be removed:

a. From at least 95% of the surfaces to be soldered of the through-hole component leads with >2.54 μm [100 μin] gold thickness and all through-hole leads that will be hand soldered regardless of gold thickness.
b. From 95% of all surfaces to be soldered of surface mount components regardless of gold thickness.
c. From the surfaces to be soldered of solder terminals plated with >2.54 μm [100 μin] gold thickness and from all solder cup terminals, regardless of gold thickness.

A double tinning process or dynamic solder wave may be used for gold removal prior to mounting the component on the assembly.

Note: Gold embrittled solder connections can occur regardless of gold thickness when solder volume is low or the soldering process dwell time is not sufficient to allow the gold to dissolve throughout the entire solder joint.

Retronix Solution

The solution is to remove the gold from the termination, using our alloy conversion process

Meets ANSI/GEIA-STD-0006
Fully automated and repeatable
Can be used for most SMT & thru hole components
ICOS, XRF & Solderability testing available inhouse for verification

Retronix have seen a steady growth in the number of customers asking us to de gild their components, initially this was seen mainly amongst our Mil/Aero customers who we have been de gilding components for historically, but this increase was seen due to the type and variety of components they were now asking us to de gild. What they had originally deemed as safe gold thicknesses on certain components were now classed as at risk of gold embrittlement and therefore sent to Retronix along with the components we were more used to seeing from them.

And this trend has expanded through to customers in other sectors who are also now using our de-gilding service when they would not have previously required the complete removal of the gold layer before assembly onto PCBs.

For more information for solutions on Gold Embrittlement please contact us by clicking here – Contact page