Ask the Experts
March 28, 2019 - 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.


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.

Reader Comment
Is there a released spec for the mask recommendations? I am guessing by the amount of responses there is very limited rules for mask other than minimum. I am using an Asymtek and it performs very well! Just have issues when the mask comes in a half mil thick or thin on a 3 mil gap flip chip. The same amount of underfill may or may not be enough or to much.
Tim Griebel, Starkey Hearing Technologies

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