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the bottom of the component. The part is then picked from the compo- nent nest on the rework machine without disturbing the deposition of the solder paste.


www.us-tech.com Reduced Cost Micro Array Component Rework


ically, a machine with a placement accuracy of 1 mil is required. Like- wise, the use of lead-free solders presents additional challenges, in- cluding decreased occurrences of self- centering during reflow and the in- ability to rely on the surface tension


al, forcing it to rise to the top of the molten liquid ball. Therefore, it is helpful to inform the paste vendor that LGAs are involved in the process, ensuring that the proper for- mulation of solder paste or flux can be recommended. Obviously, the proper application of an appropriate reflow profile minimizes the possibil- ity of voids. The reflow profile for LGA components is the same as for


Misalignment, on the other hand, can be caused by a range of place- ment and handling problems. Because the solder joints are in-


accessible for single joint touchups and visual inspection, array devices often are the defect culprits on failed assemblies. Thus, it is critical that the rework process be carefully de- veloped and performed with equip- ment that provides repeatable


March, 2013


Micro array rework requires the right tools. During the rework of LGAs, sol-


der paste volume is critical for long- term reliability. Stencil thickness and aperture sizes can be calculated for optimum solder volume. Consult manufacturers’ data sheets to deter- mine the appropriate paste volume needed for long-term reliability.


Placement Featuring smaller ball sizes and


finer pitches, µBGA and LGAs re- quire more accurate placement. Typ-


of the solder self-centering the device as in the past with standard, leaded BGAs.


Reflow The next significant concern as-


sociated with solder paste used in the LGA process is that of potential voids in solder joints caused by the flux material. Typically, these voids occur near the body of a LGA because the flux is lighter than the solder materi-


Tolerances of 1 mil are required for placement systems to ensure proper component positioning.


any surface mount device and the ideal reflow temperature is 235°C. With µBGAs and LGAs, the na-


ture of the defect types is quite simi- lar to other SMT devices: solder bridging, cold solder joints or mis- alignment. In the case of defective joints, potential causes include defec- tive solder balls, poor solder and/or flux quality, poor solder paste and/or flux deposition, unclean solder pads, or improperly applied reflow profiles.


face time


process control. The necessary re- work process steps follow:


l Reflow (for removal) l Site preparation


l Solder paste or flux deposition l Placement l Reflow


Reflow: The application of a uniform, repeatable reflow profile is crucial. The heating process must cause the


Continued on next page


To Be Precise. Innovators in Wire Processing


RotaryStrip 2400 - Fully Programmable Rotary Wire Stripping Machine Wire sizes from 36 - 10 AWG and jacketed cables up to 0.275” (7mm) in diameter can be processed, providing the highest precision and quality available on the  - ness, make the RotaryStrip 2400 a wise investment for the future.


Intuitive color touch screen user interface No blade changes or mechanical adjustments required when changing wire sizes  LED lighting provides the operator with a clear view of the entire working area Controlled twisting of inner conductors


Schleuniger, Inc. | Manchester, NH | (603) 668-8117 | www.schleuniger-na.com/rs2400_us


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