PCB007 Magazine

OCTOBER 2025 I PCB007 MAGAZINE 43 using immersion gold technology, as well as newer gold plating technologies such as reduction assisted gold. As a result, the fabricator must do more work to ensure an IPC 4556A-compliant ENEPIG deposit. IPC-4556A: Tighter Control on ENEPIG Gold Thickness IPC-4556A retains the same thickness specifications as previous versions for all three deposit layers: • Electroless nickel: 3 to 6 µm ± 3 standard deviations from mean • Electroless palladium: 0.05 to 0.3 µm ± 3 standard deviations from mean • Gold: 0.03 µm min ± 3 standard deviations from mean, 0.070 mm max Nickel and palladium tolerances are easy to achieve. Gold, however, presents the greatest chal- lenge, with the tightest specification range and more contributing variables than ENIG. The mini- mum gold thickness was based on round robin test- ing (IPC-4556, 2013) to ensure soldering and wire bonding performance. The maximum limit, defined in Amendment 1 (2016), prevents higher gold thick- ness deposition and corrosion risks using galvanic displacement/immersion gold systems. Maintaining ENEPIG gold thickness involves more contributing variables than ENIG, meaning more statistical process control (SPC) requirements are needed to maintain the tighter 4556 ENEPIG thick- ness tolerance. IPC-4556A's gold range for ENEPIG is just 1.6 µin, compared to 2.36 µin for ENIG in IPC-4552B. Maintaining this tighter range requires robust SPC and careful management of measure- ment system error (MSE). Following IPC-4552B, repeatability of XRF mea- C o l l i m ato r X R F g o l d t h i c k n e s s d at a eva l u at i o n u s i n g re q u i re d g u a rd b a n d s . ▼ Po l y- c a p i l l a r y X R F g o l d t h i c k n e s s d at a eva l u at i o n ( n o g u a rd b a n d s re q u i re d ) . ▼ E N E P I G g o l d t h i c k n e s s c a p a b i l i t y- b a s e d o n c o l l i m ato r t y p e X R F. ▼ E N E P I G g o l d t h i c k n e s s c a p a b i l i t y b a s e d o n p o l y- c a p i l l a r y t y p e X R F. ▼

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