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Method for WSNPC pins and IHS pins for improved solder-joint reliability

IP.com Disclosure Number: IPCOM000130470D
Publication Date: 2005-Oct-25
Document File: 7 page(s) / 403K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for wave soldered nickel-plated copper (WSNPC) pins and integrated heatsink (IHS) pins for solder-joint reliability (SJR). Benefits include improved functionality, improved reliability, and improved ease of implementation.

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Method for WSNPC pins and IHS pins for improved solder-joint reliability

Disclosed is a method for wave soldered nickel-plated copper (WSNPC) pins and integrated heatsink (IHS) pins for solder-joint reliability (SJR). Benefits include improved functionality, improved reliability, and improved ease of implementation.

Background

              Flip-chip ball-grid array (FCBGA) package technology has increased the number of power, ground, and signal pins included in the package. This increase has been made possible by decreases in the ball placement pitch, the diameter of the individual solder balls, and the pads between the package and the printed circuit board (PCB). As a result, an increase has occurred in the stresses at the solder-joint interfaces and SJR has decreased.

              Solder joints are more prone to failure when a package is subjected to excessive mechanical stresses from board bending/flexure or deflection. A package that passes test after PCB assembly has a high possibility of failing. The board can bend due to shock and vibration during shipping and transportation or any situation where mishandling occurs (see Figure 1).

      Solder-joint failure is conventionally solved using the following techniques:

•             Increasing the solder ball diameter. However, this solution can lead to solder bridging electrical-short failures with fine BGA pitches.

•             Increasing the package solder resist opening (SRO) and board pad size while maintaining the optimum aspect ratio. However, this solution uses PCB surface area required for high routing density, especially with fine BGA pitches.

•             Depopulating corners of the BGA ball pattern or adding sacrificial (nonfunctional) solder balls. However, this solution restricts package routing (see Figure 2).

•             Evaluating new fluxes to improve solder-joint metallurgy, such as controlling the spread of the intermetallic compound and eliminating the phosphorus-rich layer where failure typically occurs. However, this solution involves extensive development processes.

      These solutions do not solve the board bending/flexure problem. However, they decrease the risk of solder-joint cracking.

General description

              The disclosed method places WSNPC pins or IHS pins in FCBGA package corners. The pins provide localized stiffening of the PCB, preventing flexure/bending during shock and vibration stress conditions and preventing solder-joint cracking.

              The key elements of the disclosed method include:

•             Wave soldered nickel-plated copper (WSNPC) pins

•             Integrated heatsink (IHS) pins

•             Substrate keep-out zones (KOZs)

•             Plated-through hole (PTH) KOZs

•             Wave-solder process to form pin solder joints

Advantages

              The disclosed method provides advantages, including:
•             Improved functionality due to providing PCB stiffening by WSNPC and IHS pins

•             Improved functionality d...