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Ask the Experts

September 19, 2026 - Updated
March 20, 2019 - Originally Posted

Is There a Spec for LDI Mask thickness?

Is there is a spec for LDI mask thickness? We build very small circuits with fine pitch small ball flip chips with very limited wet out area for the underfill. We have a very controlled underfill dispenser, but the gap (typical 4 mil) can vary with the mask thickness up to 30+%. If the mask comes in thick, the gap is reduced and the set volume of underfill has difficulty flowing and extends past the wet out area.

T.G.

Expert Panel Responses

The generally accepted spec for LDI mask thickness is dependent upon the copper thickness within the circuit. For example these are recommended guidelines:

Copper Thickness Min/Max Mask Thickness
35µm 5µm - 15µm
50µm 5µm - 15µm
75µm 5µm - 15µm
105µm 5µm - 20µm
140µm 5µm - 20µm

You might also want to consult your underfill dispenser supplier for their recommendation. I would also suggest contacting Nordson Asymtek as they have extensive experience with numerous dispensing applications including underfill.

Carlos Bouras
General Manager, Nordson SELECT

Carlos Bouras is the General Manager of Nordson SELECT and has over 30 years of experience in the electronics manufacturing industry. Carlos's expertise is in process engineering, product development and manufacturing operations. For the past 15 years Carlos has focused specifically on automated assembly issues and is the holder of several US patents for non-contact dispensing and precision dispensing of adhesives for the packaging of microprocessor devices.

Contact FTG Circuits Corporation in Minnetonka, MN. They have special processes for LDI to ensure the cured thickness of the solder-mask correlates to the printed wiring board thickness. They also are expert in using other mask types to meet your precise underfill needs, thus helping reduce or even eliminate excessive squeeze-out, underfill voiding and tunneling, so there are no exposed conductors under the flip chips/BGAs, CGAs, or CCGAs. They are experts at applications for microminiature HDI. Very reasonably priced, I might add. We have had really good experiences with them.

Richard D. Stadem
Advanced Engineer/Scientist, General Dynamics

Richard D. Stadem is an advanced engineer/scientist for General Dynamics and is also a consulting engineer for other companies. He has 38 years of engineering experience having worked for Honeywell, ADC, Pemstar (now Benchmark), Analog Technologies, and General Dynamics.

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