Area-array packages

Component-specific illumination panuneters are necessary for ball/bump inspection and centering of area array packages. 

Improved adhesion avoiding delamination in area-array packages... 

Anson, S. J., Failure Analysis for Area-Array Packages, High Density Interconnect (Sep. 2001)... 

K. Gilleo, Area Array Packaging Handbook Manufacturing and Assembly, McGraw-Hill Professional, New York 2001. 

FIGURE 3.9 Perimeter PO package vs. area array package. 

The next step down from area array packages is DCA. The methods of attaching a semiconductor die directly to an interconnect board (PCB, mnltUayer ceramic, etc.) are ... 

At the inception of area-array technology, the size and pitch of the I/Os were initially higher when compared to what was then 0.4 mm and 0.5 mm fine-pitch, peripherally leaded packages. However, as I/O counts have increased with the functionality of area-array packages, solder ball size and pitch have decreased significantly, particularly when taking into account DCA technology. 

The typical pitch size is 1.27 mm and 1.0 mm for BGA and CSP packages. Here, the pitch is the distance between the center points of any two balls or lands. Therefore, alignment requirements are not very stringent for these area-array packages. Also, there is a sufficient quantity of solder to allow self-aUgnment between the package and circuit board pads by the surface tension of the molten solder. However, as ball counts reach several thousands, reduced ball... 

Capabilities 1. Handle both chips and small area-array packages. 2. Moving turret and PCB to increase placement speed. 3. Flexibility of using either tape or bulk part supply. 

FIGURE 40.21 Gantry architecture used for placing larger components such as SOICs, PLCCs, and area-array packages. (Photo courtesy of Universal Instruments.)... 

Hot air or hot gas (nitrogen) has been used to reflow, simultaneously, all solder joints of fine-pitch (high I/O count), peripheral leaded packages (e.g., QFPs) as well as those of area-array packages that include EGA component CSPs, and FC components. An example of a hot-gas nozzle apphed to a EGA package is shown in Fig. 40.31. Control of the hot-air flow maximizes heat dehvery to the solder joints and minimizes the temperatnre rise in the component body. The shroud also limits the exposure of neighboring devices and their solder joints to elevated temperatures. 

Inspection. Visual inspection should be conducted as practical to ensure integrity of any visible solder joints and also the area surrounding the rework. Ensure that solder mask is not charred or delaminated. Also check whether bonding pads have delaminated (not possible on inner rows of area-array packages). 

A number of lead-free component termination finishes have been evaluated (Ref 13, 55) and used over the years. For passive components (such as chip capacitors and resistors), matte Sn plating has been used for many years with the tin-lead solder, and can be used with lead-free solder as well. For leaded components (e.g., quad flat pack or QFP), plating of matte tin or tin alloys may be used with lead-free solders (forward compatible). The tin whisker concern will be discussed in a later section. Nickel-lead has been used with the tin-lead solder for many years, and Ni-Pd-Au is currently an alternative for leaded components for lead-free soldering Ni-Pd typically does not provide as good wett-ahifity as tin. Area array packages with SAC halls are available and work well with the SAC solder. 

Rework for lead-free solders has been found to be more difficult, because the lead-free solder alloys typically do not wet or wick as easily as the Sn-Pb solder due to their difference in wettability. This can be easily seen with QFP packages. In spite of these differences, successful rework methods (both manual and semi-automatic) have been developed (Ref 74-75) with lead-free solders (Sn-Ag-Cu, or Sn-Ag), for many different types of components. Most of the rework equipment for tin-lead can still be used for lead-free solder. For area array packages, it is helpful to use a rework system with split vision and temperature profiling features. The soldering parameters must be adjusted to accommodate the higher melting temperature and reduced wettability of the lead-free solder. The other precautions for tin-lead rework (such as board baking) still apply to lead-free rework. 

The issue of component mixing, or cross-contamination, warrants special concern, especially during the industry-wide transition to lead-free. If a tin-lead solder board is to be repaired (for example for warranty repair at some fiiture time) with a lead-free solder, the reliability of homogeneously mixed lead-free solder and tin-lead solder is probably not inferior to the tin-lead solder in most cases however, the temperature impact on the components (especiily plastics package parts) could be a concern. Carefol consideration must be given to the use of area array packages with lead-free balls to repair a tin-lead... 

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