TempKoat® P Plating Compatibility

This application note evaluates TempKoat® P plating compatibility with gold, nickel, and tin plating media, demonstrating chemical resistance, high aspect ratio patterning, and clean resist removal.

Overview

TempKoat® P is a chemically amplified, positive tone, temporary resist formulated for advanced packaging and MEMS applications. Specifically, TempKoat® P is capable of producing high aspect ratio features from thick, single coatings. The unique combination of resolution, excellent chemical resistance, and residue-free removal make it ideal for critical electroplating applications.

Application

TempKoat® P is a versatile resist used for plating applications spanning RDL, wafer bump, and beyond. Plating is an electrochemical deposition method with the following steps in Figure 1.

TempKoat P plating process flow from seed layer deposition through resist removal — Figure 1. Process flow for TempKoat® P. (a) Substrate with metal seed layer (b) Substrate coated with TempKoat® P (c) TempKoat® P is patterned (d) Exposed areas are developed away (e) Metal is plated in patterned areas (f) TempKoat® P is removed, leaving plated metal behind.

This method enables clean, targeted fabrication of metal features without the need to etch back unwanted material. The deposition of different kinds of metals necessitates the photoresist to withstand a wide range of harsh chemical environments. TempKoat® P is compatible with various plating media including, but not limited to copper, gold, nickel, tin, and more. This note highlights TempKoat® P’s compatibility with Au, Ni, and Sn, specifically Technic’s Elevate® Au 7934, Elevate® Ni 5950, and Elevate® Tin D5011. For more information on Cu plating, see the TempKoat® P Technical Data Sheet.

Key Features

Broad film thickness range
3:1 height-to-width aspect ratio
Fine pattern fidelity and reliability
No rehydration delay or latency post exposure
Excellent chemical resistance
Compatible with various plating media
Easy removal

Processing Guidelines

Processing Guidelines for Ni and Sn
Coat	Dispense 1 mL/inch of substrate Spin at 3,000 rpm for 30 sec
Soft Bake	3 min @ 120°C
Exposure	350 mJ/cm² (at 365 nm) Verify dose for your specific tool and filter set-up
Post Exposure Bake	2 min @ 120°C
Development	4x 60s puddles with TMAH Developer
Plating pre-treatment	Rinse with DI Water 2 minutes in Elevate Cu 6300 Cleaner – 90°F (23°C) • 15% v/v in DI Water Rinse with DI Water 1 minute in Sulfuric Acid 10% Rinse with DI Water

Table 1. Processing Guidelines – TempKoat® P on Cu Substrate for Ni and Sn Plating

Processing Guidelines for Au
Coat	Dispense 1 mL/inch of substrate Spin at 3,000 rpm for 30 sec
Soft Bake	3 min @ 120°C
Exposure	150 mJ/cm² (at 365 nm) Verify dose for your specific tool and filter set-up
Post Exposure Bake	2 min @ 95°C
Development	4x 60s puddles with TMAH Developer
Plating pre-treatment	Rinse with DI Water 2 minutes in Elevate Cu 6300 Cleaner – 90°F (23°C) • 15% v/v in DI Water Rinse with DI Water 1 minute in Sulfuric Acid 10% Rinse with DI Water

Table 2. Processing Guidelines – TempKoat® P on Au Substrate for Au Plating

Metal	Plating Solution	pH	Temperature	Current Density (ASF)	Time (min)
Gold	Elevate® Gold 7934	5.8 – 6.4	122°F (50°C)	3	30
Nickel	Elevate® Nickle 5950	4.5 – 4.9	125°F (52°C)	20	13
Tin	Elevate® Tin D5011	< 0.5	77°F (25°C)	20	6.5

Table 3. Process conditions used to plate the Au, Ni, and Sn on the substrates

When processed using the above conditions, metal plating and removal were successful. The extractables were tested using HPLC from each plating bath and found to be below detection, making TempKoat® P a robust choice for a variety of plating chemistries (Table 4). See Figure 2 for SEM of various feature types post-plating and post-removal using Au, Ni, and Sn.

Solution	Temperature (°C)	Time (hr)	Extractables
Elevate Gold 7934	50	24	Below Detection
Elevate Ni 5950	52	24	Below Detection
Elevate Tin D5011	25	24	Below Detection

Table 4. HPLC results table of extractables from TempKoat® P in plating media at temperature for 24 hours

SEM images of gold, nickel, and tin plated features before and after TempKoat P removal — Figure 2. SEM images of Au, Ni, and Sn features before and after liftoff using 15 μm thick TempKoat® P as a plating mask.

Industrial Relevance

Gold, nickel and tin are among the most prevalent finishes throughout the semiconductor industry, each one valued for different properties. Electroplated gold has high conductivity and mechanical wear resistance making it very useful for wire bonding, connectors and switches.[2] Nickel on the other hand is valued for its ability to act as a barrier between different device layers through extreme temperature swings.[1] Lastly, Tin has strong anti-corrosive properties as well as high electrical conductivity and solderability which make it ideal for making highly reliable electrical connections.[3]

Importantly, each metal requires a different plating media which typically contain harsh chemistries. The often cyanide-based plating media of gold has a strong affinity for gold ions which limits the speed of plating and necessitates long plating times.[4] Nickel plating media must be tightly controlled and free of contamination to control the stress, purity and reliability of the deposition. Tin plating media is often extremely acidic with pHs below 1. These difficult conditions require a plating resist that can withstand harsh environments without degrading, deforming, or delaminating. TempKoat® P is shown to be a robust resist when exposed to various plating media and enables these critical metallization processes for semiconductors, MEMs, and other devices.

References

[1] E. Shalyt et. al. ECS Meeting Abstracts, MA2014-02 1714, (2014). DOI 10.1149/MA2014-02/33/1714
[2] Y. Okinaka and M. Hoshino, Gold Bulletin, 31, 3-13 (1998) https://doi.org/10.1007/BF03215469
[3] Noble Metal Coatings Inc, Primary Applications of Tin Electroplating in Electronics, (2024).
[4] R. Morrissey, Technic Inc. Gold and Silver Plating Basics, Products Finishing, (2011).