Ball Grid Array (BGA) packages become increasingly more popular, impor

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Ball Grid Array (BGA) packages become increasingly more popular, impor

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Layout Recommendations Packages
Ball Grid Array (BGA) packages become increasingly more popular, important understand they affected various board layout techniques. This document provides brief overview layout considerations when working with packages. outlines some most common problems provides tips avoiding them design stage.
Disadvantages
primary drawback packaging inability access solder joints testing inspection later section this document provides layout recommendations testing). best, only outermost balls seen, board size other components often restrict even that view. best option available complete inspection device X-ray. this means, user visually assess shorted connections, missing balls, filled vias, some cases opens (see Figure Opens partial opens (where solder entire pad) more difficult require higher resolution equipment.
Advantages
greatest advantages packaging over other technologies that supported with existing placement assembly equipment. Most other package types require upgraded processes, handlers design methodologies. Incorporation BGAs requires little more than crash course layout methodologies. BGAs also offer significantly more misalignment tolerance, less susceptibility coplanarity issues easier signal routing under package (see Figure
Layout
Both types layout, Solder Mask Defined NonSolder Mask Defined (SMD NSMD respectively), have been successfully applied applications. Each layout type offers some advantages over other either recommended, depending source.
Figure Misalignment Balls Leads
Ball Leads
Solderable
0.12
0.12
Ball Leads
Solderable
0.24
0.24
bgarecc_01
February 1999
Layout Recommendations Packages
Figure Example Defects Appear X-Ray
Solder short Normal solder joint
Non-Solder Mask Defined Pads
NSMD solder mask does overlap edge copper; thus size copper defines size pad. While this technique lacks some adhesion strength pad, produce more uniform solder leveled surface finish leave more room between pads signal routing. majority packages designs type pads added strength, however NSMD pads gaining popularity. Generally best stress results come when size matches size package pad. sure check specific information package being used.
Missing solder ball Solder-filled
Plated Through Hole Placement
Probably most critical aspect layout consideration Plated Through Hole (PTH) placement. close hole, there solder mask covering via, then possible ball solder paste melt wicked into hole. enough solder lost into hole, result could open that lead. While this type defect usually detected X-ray, best avoided layout (see Figure
Solder Mask Defined Pads
pads, solder mask comes over edge copper trace (see Figure This adds element strength reasons. First, solder mask overlap provides extra strength adhesion bond between copper glass/epoxy laminate. Second, because copper needs extend beyond edge solder mask, actual copper area larger. This provides additional copper surface which laminate adhere. This added strength important cases where pad-to-PCB attachment could fail board flexing excessive temperature testing. Unfortunately, larger copper area also drawback since leaves less space between pads routing signal traces. While this generally serious problem, more likely occur when signals assigned pins that near center large matrix BGA. Therefore, suggested keep many assignments possible towards periphery device.
Geometries
geometries shown Figures typically circular. However, with standard round pad, X-ray soldered package looks same regardless quality wetting achieved; that shows outline ball. adding slight variation shape dimple (Figure possible better X-ray view check opens. When dimple feature used, solder wets entire surface ball deforms shape pad. This deformity visible X-ray. viewer must, however, learn differentiate between fully that simply solder paste residue.
Figure (Left) NSMD (Right)
Copper Solder mask
Layout Recommendations Testability
Since impossible probe pins directly, design layout techniques that bring several strategic pins test points will allow testability internal logic implementation. This simple solution combined with ispANALYZERsoftware utility provide full accessibility testability package. ispANALYZER lets user bring internal macrocells
Laminate
Layout Recommendations Packages
Figure NMSD Dogbone with Typical Dimenstions Most 1.27mm Pitch PBGAs
diameter drilled diameter finished diameter) trace width
Figure with Example Dimensions
solder mask opening diameter
solder diameter
solder mask overlap
solder mask clearance 35.4 mils
Solderable surface
Solder mask over copper
solder diameter
Solderable surface
Solder mask over copper
Bare laminate
solder mask opening diameter
other macrocell outputs) unused pins. With this capability, suspect tested test point that designed bring number predefined pins. Another option make Lattice ispGDXor ispGDSswitch matrix device. These devices designed route signals, allowing pinout change without affecting layout board. routing some traces through complete flexibility pinout device. ispGDX ispGDS device especially powerful when used conjunction with ispANALYZER utility. Figure Examples Solder Bumps (Also Called Dimples Ears)
additional information Lattice ispGDX ispGDS devices ispANALYZER software utility, contact your local Lattice sales office Field Application Engineer, visit Lattice Semiconductor website http:\\www.latticesemi.com.
Conclusion
Armed with simple layout tips, most difficulties switching from package overcome. packages tolerant misalignment with help X-ray machine easy spot manufacturing defects guarantee high quality.

Ball Grid Array (BGA) packages become increasingly more popular, impor

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