Application Note CONTENTS 3.1.1 3.1.2 3.1.3 3.1.4 INTRODUCTION Te
|
|
|
Top Searches for this datasheet
(LF)BGA APPLICATION NOTE INNOVATION, PHILIPS SEMICONDUCTORS MARCH 2000
Application Note
CONTENTS 3.1.1 3.1.2 3.1.3 3.1.4 INTRODUCTION Technology boundaries. OUTLINE VERSIONS REFLOW SOLDERING PROCESS Stencil printing Filling apertures Levelling Stencil release Print results Component placement Reflow soldering FOOTPRINT DESIGN Print board dimensions pattern positions Component placement Reliability. Routing PROCESS WINDOW Stencil printing Reflow soldering REWORK Device removal Site separation Device replacement (LF)BGA FOOTPRINTS Ball pitch 0.50 ball diameter 0.32 Ball pitch 0.80 ball diameter 0.46 0.40 Ball pitch 1.00 ball diameter 0.50 Ball pitch 1.27 ball diameter 0.75
Application Note
INTRODUCTION Process characteristics Base material: FR4/polymide Finish: Ni/Au Solder paste (e.g.): Alpha metals LR735 LFBGA Stencil thickness: uniform (for LFBGA with pitch stencil will result larger process window) Process: double-sided reflow Printing accuracy: Operator knowledge: advanced training Process capability Overall failure (95% confidence level solder joint) OUTLINE VERSIONS
plastic Ball Grid Array (BGA) profile Fine pitch (LFBGA) packages have developed over recent years from being rarely used devices, become, many applications, first choice designers requiring medium high pin-count packaging. When comparing other common alternative packages, such Quad Flat Pack (QFP), (LF)BGA device many clear advantages. Such (LF)BGA easy-to-bend leads that cause deviation from coplanarity. (LF)BGA typically smaller than equivalently functional QFP. Resolution smearing problems with respect stencil-print process less because pitch larger, apertures circular. self-alignment property component results large process window automatic placement. (LF)BGA compatible with today's assembly techniques, which means that adjustments necessary standard machines materials. This application note describes status technology February 2000. continuous improvements material processing board assembly, specifications example, substrates change over time. Technology boundaries
Philips Semiconductors offers several (LF)BGA outline versions with different count, pitch body dimensions. overview current range show Data Handbook IC26: Integrated Circuit Packages. This application note contains aspects processing (LF)BGA, including footprint design, stencil printing, automatic placement, reflow soldering process rework. REFLOW SOLDERING PROCESS
most important items (LF)BGA technology shown below. Printed circuit board conductor lines: spacing: solder resist resolution: placement accuracy: 62.5 LFBGA multilayer
reflow soldering process comprises three steps: Stencil printing Component placement Reflow soldering.
Application Note
Stencil printing
squeegee solder paste stencil solder land
(LF)BGA assembly, stencil printing most critical process step. This because that, after soldering, joints cannot inspected case with other surface mounted devices.If balls properly soldered, only detected using electrical testing, X-ray destructive analysis. Stencil printing divided into three sub-processes: Filling apertures Levelling Stencil release. These three steps shown Fig.1. 3.1.1 FILLING APERTURES
board
filling
filling apertures determined complex interaction between material properties stencil squeegee, solder paste machine settings, such pressure speed. ensure apertures properly filled, solder paste must "roll" stencil front squeegee. rolling paste, highest pressure arises point where squeegee contact with stencil. This place where solder paste flow into stencil apertures. 3.1.2 LEVELLING
levelling
elevating force squeegee determines whether squeegee correctly levels paste stencil openings. This force determined factors such amount paste, squeegee angle stiffness, print speed, applied pressure squeegee. last two, which machine parameters, controlled operator until satisfactory result obtained. process window increased ways: increasing pressure squeegee and/or using stiff squeegee. example, increasing pressure above level that simply required clean stencil ensures sufficient paste forced through stencil aperture onto solder land, which turn increases process window. Likewise, using stiff squeegee increases process window. However, careful balance maintained because squeegee stiff, would able follow shallow contours board. Refer Section more information process window.
release
MSB905
Fig.1 Applying solder paste stencilling
Application Note
3.1.3 STENCIL RELEASE Component placement
When apertures filled with solder paste, stencil board separated. separating determines smallest printable opening. Though experimentation, have found that stencil printing combination with slow, controlled release speed gives best results, compared with printing with zero snap-off. highest resolution obtained separation speed slow with small "jerks". This ensures that excess paste removed from apertures caused resulting vibrating motion. 3.1.4 PRINT RESULTS
factor component placement size component. example, small passive components usually placed with chip shooter, whereas larger components, such ICs, placed with placer. (LF)BGAs considered large components, irrespective their actual size. major process deliverable placing machine speed placement accuracy. latter which determined vision alignment system. addition, placement force also important ensure optimum contact. high force component crack damage solder land; force component will have poor contact with solder paste.
circular stencil apertures relevant. Figure shows typical appearance solder paste deposits diameter stencil openings increase. Also, owing process vibrations, deposition look different even when using only stencil opening.
handbook, full pagewidth
Stencil thickness
MGS886
paste. Irregular shape (few balls). Pyramid lower than stencil thickness. Pyramid larger equal stencil thickness (acceptable). Beginning flat with "dog ears" (preferable). Flat topside (preferable). Scooped-out bulldozed.
Fig.2 Different deposition appearances with increasing stencil opening diameter.
Application Note
Reflow soldering important note that this profile based properties printed circuit board solder paste. each component board specific profile (see example Fig.4), components profile must superimposed board's profile give true representation particular product's process window (see Fig.5). Note: temperatures measured solder joint.
During soldering, metal pads joined molten solder that flows between their adjacent surfaces, which have higher melting point than solder itself. parts joined, solder paste heated that flux remove oxides. After this, solder then brought above melting point. solder melts, flows around ball contacts forms meniscus. After solidification, final joint formed. achieve suitable soldered joint, parts board must subject accurate temperature/time profile. Figure shows suitable profile framework.
handbook, full pagewidth
temperature
damage
organic finish affection
time
MGS889
Tpmin
min, possible (else min) Tpmax soldering first side double-sided board with organic finish Tpmax other cases.
Fig.3 Reflow soldering process requirements boards paste.
Application Note
dbook, full pagewidth
temperature
time °C/s
MGS890
Tpmin Tpmax
Fig.4 Process window specific component.
handbook, full pagewidth temperature
damage
organic finish affection
time
MGS891
Fig.5 Example narrowed process window because component restrictions.
Application Note
FOOTPRINT DESIGN Component placement
important step design printed circuit board choice footprints. well-chosen footprint basis reliable solder joint. Print board dimensions pattern positions
(LF)BGA package owes much popularity fact component self aligning, i.e. during reflow, (LF)BGA that been properly placed, will float back optimal position solder lands thanks surface tension forces (see Fig.6). maximum displacement e.g. BGA256 LFBGA64 Furthermore, (LF)BGA does have leads that bent, placement force have large tolerance roughly between BGAs, between 1.25 LFBGAs. This force dependent board support construction placement force-control unit.
accuracy which conductive pattern positioned relative fiducial marks important factor footprint design. large tolerance pattern position results large footprint, limits number components that assembled board. maximum standard dimension printed circuit board maximum deviation distance between position fiducial mark conductive pattern processed board relative data 0.04 0.05%, whichever larger. finest pitch that can, therefore, processed within such technology
handbook, full pagewidth
reflow
MGS888
Fig.6 (LF)BGAs correctly positioned during reflow soldering.
Application Note
Reliability Routing
Experimentation shown that larger standoff height component, more reliable solder joint. method increasing this height choose layout that defined solder resist rather than etched copper (see Fig.7). seen that solder resist opening determine standoff height. resist thickness standard process technology defined being influence limited. However, play role, particularly small (LF)BGAs. It's known that connection balls directly beneath edges experience maximum stress. What known, however, whether footprint design improve stress distribution over solder joints. have found from simulations that solder joints that have same solder land board component more reliable. therefore, preferable have symmetrical solder joints. recommend, especially small (LF)BGAs, copper-defined solder lands. This because: more space available tracks running between solder lands standard copper-defined fiducials used.
best situation would that which tracks routed copper layer. This implies that inner tracks must routed between solder lands outer row. This number inner tracks permissible depends board specification footprint design. print board specification standard technology stipulates that minimum track width conductor spacing accuracy solder resist application with respect copper pattern 0.075 none, enough, track routed between solder lands, tracks have routed along vias. minimum land standard technology, number vias that placed array determined footprint design.
handbook, full pagewidth
MGS887
Fig.7 Different solder joint layouts solder resist defined copper etched defined.
Application Note
PROCESS WINDOW Stencil printing REWORK
assembly printed circuit boards, requirements after been placed solder paste that leads terminations case leadless components) must contact with solder. This because lead contact with paste, then wetting lead liquid solder always good. practice, this means that solder pasted deposits should have same height, i.e. their height should equal stencil thickness (see Fig.2). fundamental difference between (LF)BGA normal that leads (LF)BGAs consist entirely eutectic solder, whereas leads standard SMDs, most cases, only eutectic tin-plating tenths microns leads terminations). Also, tolerance coplanarity (LF)BGA package larger than with comparable amount input outputs. maximum coplanarity tolerance BGAs QFPs non-coplanarity some termination balls will touch solder paste, even thick stencil used. This because ball will pressed into paste depth only Reflow soldering
Although (LF)BGA assembly yields very high, there still requirement component rework. rework, mean process removing component from replacing with component. (LF)BGA removed from pcb, solder balls component deformed drastically removed (LF)BGA discarded. Device removal
case with component, essential when removing (LF)BGA that board, tracks, solder lands surrounding components damaged. remove (LF)BGA, board must uniformly heated temperature close reflow soldering temperature. uniform temperature reduces chance warping pcb. this recommend that board heated until certain that joints molten. Then carefully pull component board with vacuum nozzle. Site separation
peak temperature reflow soldering should remain below (typically peak temperature between dwell time above should exceed seconds, with preference temperatures higher ends permit good wetting ball shear. moisture present plastic package during soldering, turn into steam expand rapidly. Under certain circumstances, force exerted this expansion cause internal delamination more severe cases, result internal external crack (known popcorn effect). avoid this problem, components should removed from their drypack longer than specified label. reflow soldering profile shown Fig.3. Although minimum peak temperature defined enlarge process window less sensitive oven temperatures, practice minimum peak temperature often defined.
When component been removed, vacant site must then cleaned before replacing (LF)BGA. Removing often leaves varying amounts solder mounting lands. This excessive solder removed with either solder sucker solder wick. remaining flux removed with brush cleaning agent. recommended that both sides board cleaned ensure maximum success. After board properly cleaned inspected, apply flux solder land connection balls (LF)BGA. apply solder paste this shown result problems during re-soldering. Device replacement
last step repair process solder component board. Ideally, (LF)BGA should aligned under microscope magnifying glass. this possible, align (LF)BGA with board markers. reflow solder, apply temperature profile that close possible profile shown Fig.4. damage neighbouring components, necessary reduce some temperatures times.
Application Note
(LF)BGA FOOTPRINTS
handbook, full pagewidth
detail
ball pitch
ball diameter
MSD412
Fig.8 Generic footprint diagram (LF)BGA.
Ball pitch 0.50 ball diameter 0.32
Fig.8. Occupied area: package outline Dimensions: copper 0.275 solder paste 0.300 solder resist 0.425 Clearance between solder lands should 0.15 packages that this footprint shown Table exact ball layout packages, refer relevant drawing Data Handbook IC26: Integrated Circuit Packages. Table PACKAGE NAME LFBGA20 LFBGA32 LFBGA48 LFBGA56 LFBGA84 LFBGA56 LFBGA64 LFBGA80 PHILIPS OUTLINE CODE SOT479-1 SOT478-1 SOT488-1 SOT516-1 SOT518-1 SOT542-1 SOT543-1 SOT557-1 OUTLINE DIMENSIONS 3.32 4.45 1.05 1.05 1.05 1.05 1.05
Application Note
Ball pitch 0.80 ball diameter 0.46 0.40
Fig.8. Occupied area: package outline Dimensions: copper 0.425 solder paste 0.425 solder resist 0.575 Clearance between solder lands should 0.15 packages that this footprint shown Table exact ball layout packages, refer relevant drawing Data Handbook IC26: Integrated Circuit Packages. Table PACKAGE NAME LFBGA96 LFBGA114 LFBGA144 Ball pitch 1.00 ball diameter 0.50 PHILIPS OUTLINE CODE SOT536-1 SOT537-1 SOT512-1 OUTLINE DIMENSIONS 13.5 1.05 1.05 1.05
Fig.8. Occupied area: package outline Dimensions: copper 0.45 solder paste 0.45 solder resist 0.60 Clearance between solder lands should 0.15 package that this footprint shown Table exact ball layout packages, refer relevant drawing Data Handbook IC26: Integrated Circuit Packages. Table PACKAGE NAME BGA256 PHILIPS OUTLINE CODE SOT466-1 OUTLINE DIMENSIONS 1.75
Application Note
Ball pitch 1.27 ball diameter 0.75
Fig.8. Occupied area: package outline Dimensions: copper 0.60 solder paste 0.60 solder resist 0.75 Clearance between solder lands should 0.15 packages that this footprint shown Table exact ball layout packages, refer relevant drawing Data Handbook IC26: Integrated Circuit Packages. Table PACKAGE NAME BGA256 BGA256 BGA292 BGA304 BGA316 BGA388 BGA492 PHILIPS OUTLINE CODE SOT466-1 SOT471-1 SOT489-1 SOT550-1 SOT531-1 SOT532-1 SOT514-1 OUTLINE DIMENSIONS 1.75 1.55 1.75 1.75 1.75 1.75 1.75
Other recent searches
Si5511DC - Si5511DC Si5511DC Datasheet
PXA27x - PXA27x PXA27x Datasheet
LA8606M - LA8606M LA8606M Datasheet
IDT70V07S - IDT70V07S IDT70V07S Datasheet
CDAE-302-001 - CDAE-302-001 CDAE-302-001 Datasheet
2SC520 - 2SC520 2SC520 Datasheet
2SA657 - 2SA657 2SA657 Datasheet
1SBD250125E1001 - 1SBD250125E1001 1SBD250125E1001 Datasheet
Privacy Policy | Disclaimer
© 2012 Datasheet Archive
