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A Low Temperature Polyimide-Based Solder Resist with Improved Toughness

IP.com Disclosure Number: IPCOM000101586D
Publication Date: 2005-Mar-16
Document File: 3 page(s) / 260K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a low temperature, low CTE polyimide-based solder resist material that meets the requirements for current and future semiconductor packages. Benefits include a solution that is compatible with high volume manufacturing processes and infrastructure, and improves margins for lead-free preconditioning.

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A Low Temperature Polyimide-Based Solder Resist with Improved Toughness

Disclosed is a method for a low temperature, low CTE polyimide-based solder resist material that meets the requirements for current and future semiconductor packages. Benefits include a solution that is compatible with high volume manufacturing processes and infrastructure, and improves margins for lead-free preconditioning.

Background

Currently solder resist cracking, and delamination after lead-free preconditioning, are a significant concern in lead-free compatible packaging. New solder resist materials with improved toughness and adhesion are required. Further, for high I/O, high-speed interconnects, the electrical characteristics and manufacturing tolerances of the solder resist plays a significant role in controlling the impedance and impedance tolerance. Solder resist materials with a lower dielectric constant and dielectric loss are required.

Current solutions focus on minimizing stress on the solder resist (e.g. using a stiff core, increasing the layer count, and other design options). Alternative solutions include using a more compliant lead-free FLI solution, such as a tin bump metallization. However, these substrate options to minimize stress make only marginal improvements, and the use of non-copper based FLI on the die poses significant integration challenges. Polyimide-based solder resist materials are typically thermoplastic, and require significantly higher cure temperatures (i.e. in excess of 250oC) to fully realize the benefits of the improved mechanical properties. These high temperatures are not suitable for organic substrates.

General Description

The disclosed method provides a polyimide-based material formulation with a low dielectric constant, low dielectric loss, and low CTE for improved reliability. The general structure of the base material formulations is shown in Figure 1. The main components are the polyimide or polyimide precursors with the corresponding diamine, dianhydride, and norbornene capped anhydride.  In Figure 1, n is chosen to balance viscosity and/or film forming properties as needed for the screen printing, roller coating, or lamination techniques. The base anhydride and amine of the polyimide precursor are chosen to balance the requirement for CTE and flexibility, and can include: PMDA, BPDA, BTDA, DSDA, BPADA and 6FDA. 

For example, depending on the application (rigid or flexible substrate), the component X is chosen to be an oxygen, carbonyl, silicone, siloxane, or carboxyl group for improved flexibility. To improve the base developer solubility, hydroxyl, carboxyl, or –CF3-C-CF3 moieties are incorporated on the polyimide backbone structure.  The –CF3-C-CF3 moiety also affects electronic polarization and yields a lower dielectric constant and low-loss solder resist material. The diamine can include: m-PDA, ODA, p-PDA, DDS, and MDA. The norbornene end cap precursor can be a nadic anhydride. Any of the associated derivativ...