Browse Prior Art Database

Enhancement of Fine Pitch Flip Chip Interconnection by Using Thin Soldermask

IP.com Disclosure Number: IPCOM000006690D
Original Publication Date: 2002-Jan-23
Included in the Prior Art Database: 2002-Jan-23
Document File: 2 page(s) / 36K

Publishing Venue

Motorola

Related People

Burt Carpenter: AUTHOR [+4]

Abstract

Enhancement of Fine Pitch Flip Chip Interconnection by Using Thin Soldermask

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Enhancement of Fine Pitch Flip Chip Interconnection by

Using Thin Soldermask

Burt Carpenter, Brian Sawyer, Bill Stone, Trent Uehling

For flip chip packages with fine bump pitches, standard solder mask thickness creates problems with assembly yields and reliability.  Yield is negatively impacted with conventional thickness by the increased difficulty dispensing underfill material into the smaller die to substrate gap created by the smaller fine pitch bumps.  The bump to substrate interconnect is also affected by the thicker solder mask creating deeper apertures for the bump to clear in order to reach the pad.  Reliability is improved by increasing the gap between the die and substrate, thus allowing more underfill to buffer the stresses.

By specifying a limited allowable soldermask thickness, below conventional thickness limits, the die to substrate gap is increased and the pad aperture depth is reduced.  These improvements will enable fine pitch flip chip packages to have higher yields and higher reliability. Figure 1 and Figure 2 illustrate these scenarios when using conventional and thinned soldermask thicknesses.

Pb37 Sn63

Bump

80 µm

Cu Pad

Soldermask

30 µm

Cu Pad

Soldermask

15 µm

Pb37 Sn63

Bump

80 µm

Figure 1. Flip chip interconnect with a                                              Figure 2. Flip chip interconnect with a

    conventional soldermask thickness                                                         thinned soldermask thickness

         The allowable soldermask thickness is determined by several variables. These variables are listed Equation 1 with an illustration of the...