14.1 Introduction plastic ball grid array (PBGA) become most popu
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Ball Grid Array (BGA) Packaging
14.1 Introduction
plastic ball grid array (PBGA) become most popular packaging alternatives high devices industry. advantages over other high leadcount (greater than ~208 leads) packages many. Having leads bend, PBGA greatly reduced coplanarity problems minimized handling issues. During reflow solder balls self-centering pad), thus reducing placement problems during surface mount. Normally, because larger ball pitch (typically 1.27 over PQFP, overall package board assembly yields better. From performance perspective, thermal electrical characteristics better than that conventional QFPs PQFPs. PBGA improved design-to-production cycle time also used few-chip-package (FCPs) multi-chip modules (MCMs) configurations. BGAs available variety types, ranging from plastic overmolded BGAs called PBGAs, flex tape BGAs (TBGAs), high thermal metal BGAs with profiles (HLPBGAs), high thermal BGAs (H-PBGAs). H-PBGA family includes Intel's latest packaging technology Flip Chip (FC)-style, H-PBGA. FC-style, H-PBGA component uses Controlled Collapse Chip Connect packaged Organic Land Grid Array (OLGA) substrate. addition typical advantages PBGA packages, FC-style H-PBGA provides multiple, low-inductance connections from chip package, well size cost benefits. providing multiple, low-inductance connections FCstyle, HPBGA offers equivalent better performance than extra on-chip metal layer. technology also provides die-size benefits through elimination bond ring better power bussing metal utilization. OLGA substrate results smaller package, since there cavity, thermal management benefits since thermal solution directly contact die.
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Ball Grid Array (BGA) Packaging
14.2
Package Attributes
PBGA Lead Count Sq/Rect. Pitch (mm) Package Thickness (mm) Weight (gm) Max. Footprint (mm) Shipping Media: Tape Reel Trays Desiccant Pack Comments/ Footnotes
(15mm)
Table 14-1. PBGA Package Attributes
(23mm)
(23mm)
(17mm)
(27mm)
(31mm)
(27mm)
(31mm)
(35mm)
(35mm)
(35mm)
1.61 15.20
1.27 2.33 1.56 23.20
1.27 2.38
1.56
1.27 2.13
1.27 2.33 3.46
1.27 2.13 2.86 27.20
1.27 2.38 3.87 31.20
1.27 2.38 5.06 35.20
1.27 2.38
1.27 2.38
23.20
17.20
27.20
31.20
35.20
35.20
Table 14-2. H-PBGA/HL-PBGA Package Attributes
H-PBGA Lead Count Sq/Rect. Pitch (mm) Package Thickness (mm) Weight (gm) Max. Footprint (mm) Shipping Media: Tape Reel Trays Desiccant Pack Comments/ Footnotes thermally enhanced with heat sinks thermally enhanced with heat sinks thermally enhanced with heat sinks thermally enhanced with heat sinks 1.27 2.54 4.52 27.2 31.0 1.27 2.13 15.25 43.0 1.27 2.54 4.11 31.0 35.0 31.10 1.27 1.54 HL-PBGA 1.27 1.54 8.90 35.10 40.10 1.27 1.54
14.3
Package Materials
PBGA package consists wire-bonded substrate made two-metal layer copper
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clad bismaleimide triazine (BT) laminate. Four-metal layer substrate designs generally contain additional power and/or ground planes improve electrical thermal performance. bonds protected encapsulated with molding compound. holes drilled through substrate provide routing from lead fingers respective eutectic (63/37 Sn/Pb) solder balls underside. Thermal performance enhanced adding heatsink fastened through mechanical means using thermal grease using conductive epoxy. H-PBGA HL-PBGA, however, configured differently provide greater thermal required, electrical performance. thermal advantage provided this design based first upon attaching bottom surface heatspeader slug that also forms topside package. Secondly, because copper heatspreader forms package, thermal resistance extremely exposes package surface available flow. required, this heatslug directly coupled active passive thermal management devices such heat sinks heat pipes. Improved electrical performance achieved through additional power and/or ground planes. FC-style, H-PBGA package consists reflowed onto oraganic substrate. substrate consists four layers copper with insulating materials between. copper layers connected vias. (Bismaleimide Triazine) resin reinforced with glass fiber forms core organic substrate. Solder bumps surface joined with solder pads (60% organic substrate reflow furnace. These joints form electrical/ mechanical connection between OLGA package. epoxy underfill fills between substrate. This underfill provides mechanical support protection dieto-package interconnects also minimizes thermal stress (coefficient thermal expansion) mismatch with substrate materials. backside exposed allowing thermal solutions thermal interface material have direct contact with surface. Figure 14-1, Figure 14-2, Figure 14-3 description PBGA, HL-PBGA, FC-style H-PBGA packages. Figure 14-1. PBGA Cross-Section
Design
Mold Compound
Non-laminate
Solder Balls
A5764-01
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Ball Grid Array (BGA) Packaging
Figure 14-2. HL-PBGA Down Cross-Section
Copper Slug/Heatspreader
Laminate
Down Design Encapsulant
Solder Balls
A5765-01
Figure 14-3. FC-Style, H-PBGA Cross-Section
Bumps Lamintate
Die-up Design Underfill
Solder balls
A7428-01
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14.4
Package Dimensions
Package Family Attributes Category Acronym Ball Counts Plastic Ball Grid Array PBGA, HL-PBGA, H-PBGA PBGA: 196, 208, 241, 256, 304, 324, 421, 468, 492, 544. HL-PBGA: 352, 304, 432. H-PBGA: 540. FC-style, H-PBGA: 495, 615. Ball Material Ball Pitch Board Assembly Type Solder (63/37) 1.0, 1.27 Surface Mount
Table 14-3. Plastic Ball Grid Array Family Attributes
Table 14-4. Symbol List Plastic Ball Grid Array Family
Letter Symbol
NOTE: Controlling Dimensions: Millimeter
Description Dimensions Overall Height Stand Encapsulant Height Height with Bumps Underfill Ball Diameter Substrate Thickness Package Body Length Encapsulant Length Package Body Width Encapsulant Width Width Length Ball Pitch Ball Count i.e. Lead Count Outer Ball Center Short Edge Body Outer Ball Center Long Edge Body
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Ball Grid Array (BGA) Packaging
Figure 14-4. PBGA Package Ball Array Configuration
Corner Corner
PBGA
PBGA
PBGA
Corner
PBGA
(17mm)
Corner
PBGA (27mm)
Corner
PBGA
Corner
A5487-03
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Figure 14-5. PBGA Package Ball Array Configuration Continued
Corner
PBGA
PBGA
Corner
PBGA
Corner
PBGA
Corner
PBGA (35mm)
Corner
A6124-02
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Figure 14-6. 15mm PBGA Outline Drawing
15.00 ±0.20 13.00 ±0.25 Corner 10.57 0.60 0.40
Corner 1.00 Places
13.00 ±0.25 10.57 15.00 ±0.20
1.00
1.00
Chamfer I.D. Places Dia. View 1.61 0.19 0.85
1.00
Bottom View Solder Balls
0.40 0.10 0.36 0.04
Seating Plane Side View
Notes: Dimensions Millimeters
A5829-01
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Figure 14-7. PBGA Outline Drawing
Corner Corner
Chamfer Places
I.D. Dia.
View
Places
Bottom View
Note: Dimensions Millimeters
Side View
Seating Plane
A5766-01
Table 14-5. PBGA Package Family Dimensions
PBGA Package Dimensions (2L/4L) 1.27 1.27 1.27 1.27 1.37 14.80 12.75 1.75 15.20 13.25 1.94 0.50 1.12 22.80 19.25 2.32 0.70 1.22 23.20 19.75 2.17 0.50 1.12 22.80 19.25 2.59 0.70 1.22 23.20 19.75 2.12 0.50 1.12 30.80 25.50 2.54 0.70 1.22 31.20 26.70
(17mm) 1.37 0.30 0.75 16.80 14.75 1.75 0.50 0.85 17.20 15.25
(27mm) 1.94 0.50 1.12 26.80 23.75 2.32 0.70 1.22 27.20 24.25
1.00
1.34 0.60 0.90
1.34 0.60 0.90
1.00 0.40 0.60
1.44 0.60 0.90
1.53 0.60 0.90
.32/.52 .40/.60 .32/.52 .40/.60 .32/.55 .40/.67 .32/.52 .40/.60 .32/.52 .40/.60
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Table 14-6. PBGA Package Family Dimensions Continued
PBGA Package Dimensions (2L/4L) 1.27 1.27 1.27 1.27 1.27 1.94 0.50 1.12 26.80 23.75 2.32 0.70 1.22 27.20 24.25 2.17 0.50 1.12 30.80 25.75 2.59 0.70 1.22 31.20 26.25 2.17 0.50 1.12 34.80 29.75 2.59 0.70 1.22 35.20 30.25 2.14 0.50 1.12 34.80 29.75 2.52 0.70 1.22 35.20 30.25 2.14 0.50 1.12 34.80 29.75 2.52 0.70 1.22 35.20 30.25
1.44 0.60 .32/.55 0.90 .40/.67
1.53 0.60 .52/.55 0.90 .60/.67
1.63 0.60 .52/.55 0.90 .60/.67
1.63 0.60 .52/.55 0.90 .60/.67
1.63 0.60 0.90
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Figure 14-8. HL-PBGA/H-PBGA Package Ball Array Configuration
Corner Corner
HL-PBGA
HL-PBGA
HL-PBGA
Corner
H-PBGA
Corner
A5832-02
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Figure 14-9. HL-PBGA Package Outline Ball Array Configuration
Corner Corner
I.D. Dia. View
Bottom View
Side View
Seating Plane
Note: Dimensions Millimeters
A5830-01
Table 14-7. HL-PBGA Dimensions
Symbol 1.41 0.56 0.60 0.95 30.90 30.90 1.27 1.53 1.67 0.70 0.90 0.97 31.10 31.10 1.41 0.56 0.60 0.85 34.90 34.90 1.27 1.63 1.67 0.70 0.90 0.97 35.10 35.10 1.41 0.56 0.60 0.85 39.90 39.90 1.27 0.95 1.67 0.70 0.90 0.97 40.10 40.10
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Figure 14-10. H-PBGA with 25.4 square Slug Outline Drawing
View Side View Slug Corner Corner
Bottom View
Seating Plane
Note: Dimensions Millimeters
A5831-01
Table 14-8. H-PBGA Package Dimensions
Symbol
NOTE: Measurement millimeters
3.59 0.40 0.95 0.60 2.00 42.30 42.30 1.27 1.56
4.10 0.70 1.10 0.90 2.30 42.70 27.70 42.70 27.70
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Figure 14-11. FC-Style H-PBGA Package Ball Array Configurations
FC-style, H-PBGA
Corner
FC-style, H-PBGA
Corner
A7458-01
Figure 14-12. FC-style, H-PBGA Outline Drawing
Substrate Keepout Outline
Label Mark
View
Corner
Bottom View
Side View
Seating Plane
Notes: Dimensions Millimeters
A7459-01
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Figure 14-13. FC-style, H-PBGA Outline Drawing
Substrate Keepout Outline
Label Mark
View
Corner
Bottom View
Side View
Seating Plane
Notes: Dimensions Millimeters
A7460-01
Table 14-9. FC-style, H-PBGA Package Dimensions
Symbol
NOTE: Measurement millimeters
2.79 2.29 0.854 0.90 1.07 31.1 27.3 0.60 1.00 34.9 30.9 10.3 17.4 1.27 1.625 0.895 0.90 1.20 35.1 31.1 2.79
2.29 0.854 0.60 0.93 30.9 27.0 11.2 1.27 0.895 0.900
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Ball Grid Array (BGA) Packaging
14.5
Package Usage
packaging used high-performance applications with high thermal electrical requirements. BGAs into smaller footprint, decreasing pitch spacing, utilizing array solder ball connections. This allows higher density connections than that conventional QFPs PGAs. result considerably smaller finished package size. general, ball grid array features shorter electrical path lengths which reduce inductance. Mechanical problems such fragile leads absent. larger spacing between solder lands provide adequate tolerances more reliable surface mounting. Some heat dissipation facilitated through substrate. These characteristics make ball grid array package suitable wide variety devices: ASICs, memory, chip sets, other products. thin profile smaller footprint make attractive option when board space major concern. Small body size packages come close chip scale package size space constrained applications. FC-Style, H-PBGA also allows Voltage Indentification through open circuit short processer substrate. These opens shorts achieved selectively depopulating some balls. Voltage Identification used support automatic selection power supply voltages.
14.6
14.6.1
Handling: Shipping Media
Mid-temperature Thin Matrix Tray
packages shipped either tape reel mid-temperature thin matrix tray that complies JEDEC standards. Typically, JEDEC trays have same outer dimensions easily stacked storage manufacturing. tray dimensions please refer Chapter this data book. JEDEC style shipping trays returnable Intel reuse. Chapter contains detailed information return addresses different types shipping trays. Intel will shipping costs associated with return.
14.6.2
Tape Reel
Tape reel handling engineered contain protect surface mount components embossed semi-conductive polystyrene carrier tapes high speed board mounting operations found many high volume board operations. packages shipped from Intel carrier tape made antistatic treated plastic. offers exceptional strength stability over extended time wide temperature variations, while same time maintaining flexibility automated equipment. cover tape used heat sealable, transparent, antistatic. loaded carrier tapes will wound onto plastic reel. carrier tape dimensions meet standards. tape reel packaging standards offered Intel many PBGA/HL-PBGA packages meet standards, 481-1, 481-2, 481-3. However, there some products shipped from Intel tape reel that have package orientation tape that different from standards. advisable that user Intel products obtain product data sheet that shows tape reel shipping details insure correct cavity orientation understood.
14.7
Moisture Sensitivity
Most PBGA components highly sensitive moisture exposure before reflow temperature
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exposure. Maintaining proper control moisture uptake components critical prevention "popcorning" package body encapsulation material. components, before shipping, baked enclosed sealed desiccant with desiccant pouch humidity indicator card. Most components classified level level moisture sensitivity IPC/JEDEC Spec J-STD-020, "Moisture/Reflow Sensitivity Calculation Plastic Surface Mount Devices." With most surface mount components, units allowed absorb moisture beyond their times their moisture rating, damage occur during reflow process. Chapter this data book provides in-depth view package preconditioning methods moisture sensitivity requirements. Please refer Chapter more information regarding moisture sensitive components classified. Prior opening shipping attempting solder reflow, moisture sensitivity packages being used should understood proper precautions taken insure that minimal time maintained. This will insure that highest possible package reliability achieved final product. previously bagged product cannot mounted before elapsed time that product, parts rebaked Chapter Another option store opened units nitrogen cabinet until needed. Placing units effectively `stops clock.' should understood that packages continue gain moisture even after board mounting. Components that need reworked must completely processed throught thermal exposures before original limits reached. this possible, time allotment ridgely followed, bake-out completed boards must accompliished before subjecting components heat rework process. Products being removed from boards that have been returned from field failure analysis, must baked before heat expousure. this step skipped, massive damage component will result, rendering useless further efforts determining cause failure.
14.8
Designing Boards BGAs
Most packages Solder Mask Defined pads package side solder ball. size typically close identical package size. This provides balanced stress during thermal cycling, which helps maximize fatigue life.
14.8.1
Solder Mask Defined (SMD)
solder mask defined (SMD) shown Figure 14-14, copper area larger than desired land size. opening solder mask made smaller than copper land, thus defining mounting pad. couple points consider with solder mask defined are:
There advantage that overlap solder mask onto copper enhances
copper adhesion laminate surface. When using resin systems where adhesion low, this important consideration.
disadvanatage pads that fatigue life shown lower then NSMD
pads through long term reliaiblity testing. Because this issue, solder mask angle edge been thinned many package designs minimize mask impingment solder ball.
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Figure 14-14. Solder Mask Defined (SMD)
Solder Mask Copper Area
A5826-01
14.8.2
Non-Solder Mask (i.e. Metal Copper) Defined
non-solder mask (sometimes called metal copper) defined Figure 14-15, solder mask opening larger than copper area. size controlled copper etch quality control. This generally less accurate than solder mask photo image control. Non-solder mask size varies more than with pad. However, because edges copper need extend under solder mask, either made larger, provided more line routing space between pads. Pattern registration also accurate copper artwork, which generally much more accurate than solder mask pattern. Vision registration copper fiducials (reference points) will give exact location site. With pads, misrepresentation error solder mask will also shift location entire site relative vision fiducials.
Figure 14-15. Solder Mask Defined (Non-SMD)
Copper Area
Solder Mask Defined
A5833-01
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14.8.3
Package Considerations
following subsections address package layout includes guidelines size, vias routing. important implement keep-out zone around BGAs rework purposes. keep-out zone distance determined type rework equipment used. Section 14.9.8 more information.
14.8.3.1
Routing Size
Many perimeter style package typically contains four five rows solder balls; such, possible route traces between pads route signals four-layer board.
When routing trace between pads, manufacturers preferred line width spacing
technology becomes limiting factor.
When routing traces between pads, traces spaces required
size. size, traces spacing used. Figure 14-15 shows routing example ball pads. Either size acceptable, decision primarily determined manufacturers preferred line width spacing technology.
When larger trace widths desired, another alternative route (mil space/mil
trace) within pads, then neck larger trace widths once have cleared component Using routing scheme shown Figure 14-16, first ball rows routed signal layer inner rows routed bottom side package substrate. this case vias required between pads. Using routing scheme shown Figure 14-10, first three ball rows routed signal layer inner routed boards bottom side. this case vias required between pads. Vias discussed Section 14.8.3.3. Figure 14-16. Board Side Routing Example
Component Edge
pitch
Plated Mask Space
Signal Layer
Trace
A5822-01
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Ball Grid Array (BGA) Packaging
Figure 14-17. Board Side Routing Example
Component Edge
pitch
Plated
Mask
Space
Trace
Signal Layer
A5823-01
14.8.3.2
Bottom Layer Routing
Figure 14-16 shows routing example solder side four-layer board. first rows (R1, routed component side, while inner rows (R3, routed board's solder side. This example shows trace widths.
14.8.3.3
Plated Through Hole (PTH) Isolation
Regardless technique used mounting pads shape definition, isolation plated through hole (PTH) from mounting important. contained within mounting pad, solder will wick down PTH. amount solder that wicks depends many factors, including finish coating variations. Because this, results somewhat unpredictable. Some solder joints unaffected, while others will starved point creating opens. worst result partially starved joint with severely reduced cross section. This joint have significantly lower fatigue life result early system failure. Because quality solder joint guaranteed control rather than inspection, designs/processes that result random distributions generally considered unacceptable, PTH-in-pad design suggested. vias located between ball pads must covered with solder mask. suggested that, minimum, vias side covered with solder mask. bottom side also covered. Figure 14-14 shows connection between ball via. This connection often referred dogbone footprint.
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Figure 14-18. Pads Vias
Solder Ball
Solder Mask Must Cover
Solder Mask Trace Plated
A5824-01
14.8.3.4
Quality Co-planarity
assembly yields mounting components influenced properties process control procedures followed manufacturer PCB. co-planarity requirements directly related package size. Typical manufacturing specifications allow 0.01 (1%) warpage. component, this would equate nearly 0.35 warpage area under package footprint. obvious that large body (>20 component, peripheral leaded BGA, would consistently solder site with this amount bow. Most responsible vendors take precautions well below 0.010 specification that recommended industry standard specifications.
14.8.3.5
Solderability Testing Components
Standard solderability test methods through-hole other leaded devices aren't suitable testing components. `dip look' process will strip much solder ball substrate surface, leaving little examine determining solder surface wettable. wetting balance will only able sample specific solder balls substrate, which acceptable method sampling, would take considerable length time whole surface high lead count devices, would still only representative unit. untestablility production packages most suppliers further develop their ball attach processes insure minimal solder oxidation occurs. some instances, this means doing test burn-in operations before ball attach. Where this impossible, means establishing stringent control over operations after ball attach that would impact solderability. These operations, which usually include electrical testing, burn-in, inspection, bake bag, shipping, storage, etc., characterized minimize oxidation solder ball damage. However, with today's fluxes controls reflow furnaces, very unlikely that board mount problems traced solder ball oxidation. proper solder type, viscosity, screen print, reflow practices followed, very high board mount yields being obtained even with product that been stored couple years warehouse shelves. Most product used within year from manufacturing date, which also limit desiccant moisture barrier bags. solderability problems persist, careful evaluation solder pads should done insure that there proper wetting occurring both sides
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connection. Soderability problems BGAs often traced oxidation pads boards.
14.9
14.9.1
Package Board Assembly
Fluxing
Most assembly done with solder paste that contains flux, however, there some companies reporting adequate results from mounting BGAs when using residue, clean aqueous clean flux. obtain high yields reliable joints this require monitoring surface insulation resistance board insure there foreign contaminates board slder ball surface that will show reliability problems later Fluxing without paste does come with disadvantages; ball reflowed with only flux will have smaller solder volume than initially attached ball. Therefore, package will result slightly (usually 0.001-0.002mils) lower standoff height from PCB. thermal cycle reliability component could slightly compromised because reduced standoff height, especially solder balls under area full array types. self centering ability decreases because smaller solder volume. formation fillet between ball board hindered ball mis-shapen there some minor imperfection with area.
14.9.2
Solder Paste
Assembly with solder paste advantages over just fluxing pads. paste vehicle provide flux necessary both solder ball surfaces enable proper soldering component board. no-clean aqueous clean solder paste with 63Pb/37Sn commonly used mounting PBGA. Typically choice solder paste determines profile reflow parameters. Most paste manufacturers provide suggested thermal profile their products which should referenced prior developing reflow process. Since balls consist solder, flux activity ball surface assured, long paste reaches ball surface. selection paste generally made entire component being assembled, driven packages. necessary, however, ensure that thermal environmental requirements paste met. average, packages need specialized solder paste. However, most solder suppliers have developed paste that minimal voiding during reflow. This paste also used components well. advisable that time limit minutes less maintained from screen pasting reflow minutes optimum) avoid paste drying affecting solderablity contribuing voids solder balls. Some manufacturers ratings hours) exposure judged using gram jars, small dots solder sitting board which considerably faster.
14.9.2.1
Paste Deposit Inspection
quality paste print single most important factor producing high yield assemblies. Defects detected after paste print require strip rescreen PCB. deviation turn into defect downstream requiring rework repair. Thus most economic area intensify process controls when beginning assembly paste screening step. Excessive volume paste will have some negative effects self centering properties (see Section 14.9.4.1) could cause yield reliability issues (shorts bridges). However,
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adequate paste thickness required compensate board warp, poor component coplanarity, achieve acceptable board reliability. Another factor yield reliability presence adequate flux. situation, such plugged stencil hole, that causes flux paste omitted severely limited lead open connection after reflow. Print misregistration excessive slumping that connects adjacent conductors (either pads PTHs) also source concern, short final result. Therefore, usually beneficial perform paste inspection step, especially during early manufacturing runs. Whether visual/microscope inspection, manual measurement, invest automated system depends volume overall manufacturing philosophy.
14.9.3
Solder Stencils
stencil thickness, well etched pattern geometry, determines precise volume solder alloy deposited onto device land pattern. Stencil alignment accuracy consistent solder volume transfer critical uniform reflow-solder processing. Stencils usually made brass stainless steel, with stainless steel being more durable. Hole designs dependant solder ball size, squeegee type, board layout, paste used. There appears single hole style that used everyone. There companies that using square, diamond, round oval shapped holes. Round holes definitely dominate design. Many companies promoting stencil with rounded corner, square hole with five degree tapered opening been shown good hole design BGAs with smaller solder balls. Thickness stencils usually (.15 range. squeegee durometer harder should used. blade angle speed must fine tuned ensure even paste transfer. Ensuring proper stencil application most important factor with regards reflow yields further process. paste materials tend when properly environmentally controlled (see14.9.2 more explanation). Maintaining diameter stencil thickness ratio least provide good print characteristics, with larger openings providing better print quality. also beneficial opening least large mounting give wide placement window. typical design might 0.028 opening 0.006 thick stencil, going over 0.024 with solder balls. printing small amounts paste onto solder mask surrounding proven problem either yield reliability.
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Figure 14-19. Typical Paste Deposit
Direction squeegee travel
Squeegee Stencil side Screen degree angle allow relief when removing screen from board Board side Screen
A5849-02
14.9.4
14.9.4.1
Placement Alignment
Placement
packages have shown excellent self-centering properties. Because this, wide variation placement location accommodated during reflow solder joints. general rule packages that placement least pad. This illustrated graphically Figure 14-16. self centering characteristics attributed surface tension which will pull component onto during peak reflow temperatures.
Figure 14-20. Ball Placement Misregistration (A4470-01)
Mounting
Solder Ball
A5825-01
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Most common placement tools used flatpack other non-discrete packages have much better accuracy than necessary, placement variability rarely issue BGAs.
14.9.4.2
Alignment
pick place accuracy governs package placement rotational (theta) alignment. This equipment/process dependent. Slightly misaligned parts (less than pad) typically automatically self-align during reflow. Self centering pads greatly reduced grossly misaligned packages (greater than pad) develop electrical shorts, result solder bridges, they subjected reflow.
14.9.4.3
Pick-n-Place Machines
main areas concern Pick-n-Place machines are:
Component body alignment Component ball alignment. Inspection component balls before placement.
Most alignment inspections done from either bottom. there defining mark bottom package, only ensure located proper position from using mark orientation indicator. Proper placement then done:
From alignment marks board (which must done stencil, Figure
14-17).
aligning bottom component using up-down vision system accurately
place balls solder paste. Because surface some packages (like HL-PBGA types) highly reflective, some side vision systems better with their inspection process they diffuse lighting source instead polarized source. round fluorescent tube type light near package light filter over polarized fixture seems enhance operation some systems.
14.9.4.4
Outline Machine Placement
Variability body dimension specification 0.10 (~4mils) worst case. same data indicates that ball location variability 0.075 (~3mils) worst case. impact alignment during placement (vision) process
package edge used determine true center component, alignment
balls within 0.075 true position.
only package edge used, alignment balls within 0.10 0.075
(0.175mm, ~6mils) true position. Given that allowable misalignment balls less width (e.g.; 12mils 24mil pad), manufacturable process achieved using only package edge (outline) alignment marks stencil machine placement, Figure 14-16.
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Figure 14-21. Alignment
Four Corner Alignment Marks Silkscreen
35mm
Alignment Silkscreen
35mm
A5827-01
14.9.5
Solder Reflow
Except semi-accurate placement packages, there special requirements necessary when reflowing components. with components, important that profiles checked board designs. addition, there multiple PBGAs board, profile should checked different PBGA locations board. Component temperatures vary because nearby surrounding components, location part board, areas package densities. Temperatures also different edge package than center. Chapter provides more in-depth look manage these types concerns. Table 14-10 provides specific parameters followed during preheat, preflow, reflow processes. Proper desiccant handling procedures should followed prior reflow insure optimal reliability final product. Chapter details. When doing second pass wave solder mixed technology components same board BGAs, insure that solder wave profile very tightly controlled. high temperature wave solder process warp board break joints topside component.
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14.9.6
Cleaning
Cleaning done with aqueous, semi-aqueous, solvent based systems, done all. With need eliminate Chloroflourocarbon (CFC) containing materials, many companies have moved using no-clean aqueous based system. proper cleaning solder flux residues other ionics left boards from assembly process necessary long term reliability finished product. clean" fluxes simply mean that there harmful residues left board that will cause corrosion damage components left board. This residue sometimes shown collection point outside contamination board surface. application, evaluation needs done remaining residue still needs removed from boards final application.
Table 14-10. PBGA/HL-PBGA Example Reflow
Zones Preheat Pre-Reflow Reflow Characteristic Description Initial heating lead/component Peak temperature Dryout solder paste activation Soak Time Time above Peak component body temperature. Cooling rate Windows/Limits C/second 100-140 -170 Seconds Seconds Maximum C/second
Cool Down
14.9.7
Process
Many factors contribute high yielding assembly process. focus areas their contributing factors highlighted Table 14-11.
Table 14-11. Essentials Assembly Quality
Solder paste quality Uniform viscosity texture. Free from foreign material. Solder paste should used before expiration date. Shipment storage temperatures maintained proper temperature. Paste protected from drying solder stencil. Clean, flat, well-plated solder ball land area. Good soldermask coverage. Tight tolerances usually required. self-center itself long major portion (more than 50%) solder ball contact with fluxed solder paste land area board. Alignment marks (targets) helpful placing parts. Know your components moisture sensitivity classification adhere IPC/JEDEC moisture control conditions package delamination cracking occur.
Motherboard quality Placement accuracy
Moisture Sensitivity Precautions
14.9.8
Rework Packages
yields packages very high, there still possible need rework components. Component defects, defects, other functional problems require rework package from PCB.
2000 Packaging Databook
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Ball Grid Array (BGA) Packaging
Rework process removing component from PCB, replacing with component. removed component immediately reusable. shape volume solder balls will same package. component reuse desired, separate process replacement solder balls should used.
14.9.8.1
Rework Tooling
There several systems currently market reworking components. Some systems direct heat under package while other systems direct package. Backside heating common feature rework tools. While some systems attempt backside heat with local behind package reworked, this often results large-scale warpage during processing, especially large. suggested method global heat that brings entire specified temperature (100-125°
14.9.8.2
Rework Processing
rework process relatively simple. biggest challenge rework requirement controlled process. Often rework accomplished with very coarse methods such hand placement soldering iron reflow. Such approaches work BGA. process used rework package understood controlled (similar initial attach), result likely additional defects additional rework. perform rework, there four basic steps: removal, site preparation, flux solder paste application, replacement/reflow. following subsections describe each.
14.9.8.3
Component Removal
package removed with tool, usually fitted with custom head that sized package. Proper sizing head reduces thermal impact adjacent packages. Correct tool settings depend tool being used, package being removed, PCB. Determining settings exercise profiling, similar initial reflow. using profile assembly with thermocouples mounted solder joints, tool settings determined which assure that solder joints reflow properly. Monitor both bottom PCB. component removed from vacuum nozzle within integral head. When profiling, shut vacuum component removed avoid damage profile card. Control pressure head down onto component during removal. pressure applied after solder balls melted, solder pressed between "plates" substrate PCB, resulting bridging that must removed manually. possible solutions are:
Establish head height prior reflow control stroke. Place shims under edges component prevent collapse
Consider effects other components. other packages near package being reworked, monitor their solder joint temperature. temperature approaches reflow temperatures, shielding necessary. Preheating assembly good practice when reworking packages. Advantages are:
reduce heating time required using rework head. cases where assembly
preheated while another reworked, cycle time greatly reduced.
More uniform profiles achieved. challenge profiling temperature spread
between center edge solder joints. Preheating reduces spread bringing baseline temperature closer reflow temperature.
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warpage minimized. Warpage caused higher local temperature site than
surrounding area. raising assembly temperature, mismatch minimized warpage reduced.
reduces problems with adjacent components, allows shorter heat times lower
temperatures used, thus reducing risk affecting neighboring solder joints.
14.9.8.4
Site Preparation
Once component removed, prepare site accept component. removal process generally leaves varying amounts shapes solder mounting pads. ensure maximum probability success, suggested that sites made uniform possible prior reattach component. Solder removal accomplished variety methods from solder wick custom solder vacuum tools desired result similar mounting surfaces across mounting pads.
14.9.9
Removal Replacement Process
removal replacement procedure PBGA package follows: Plastic Ball Grid Array Package Removal from Board. Preheat board minimum temperature (max. temperature 220° part board over 160° C-170° close solder melting temperature 183° risks damaging joints other components board, especially bottom side parts which closer heat source. recommended that each manufacturer conducts time temperature experiments determine optimum conditions minimize board/package warpage. Monitor both bottom-side board temperatures. Dispense liquid, no-clean flux between package board. Attach vacuum pick-up onto package apply (preheat, ramp time, temperature determined manufacturer's experimentation). Note that some cases mother-board lifting problems have been reported possibly machine type used much upward tension there vacuum pick-up. This problem solved manufacturer determining typical time release when using vacuum pick-up, adding seconds then applying vacuum pick-up during removal until this amount time passed. Lift package from board. Turn carefully remove board from heat source allow cool safe, handling temperature. Inspect board determine damage occurred adjacent components board itself. Inspection, Preparation Replacement Package Remove excess solder from PBGA solder pads using solder wick vacuum. Clean PBGA solder pads with alcohol brush. Allow board inspect ensure clean surface. Preheat board minimum temperature part board over 160° C170° really close solder melting temperature 183° risks damaging joints other components board, especially bottom side parts which closer heat source. advised that each manufacturer conduct temperature experiments determine optimum conditions minimize board/package warpage. Monitor both bottom-side board temperatures.
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Ball Grid Array (BGA) Packaging
stenciled solder paste optional (and PBGA packages larger, required). applications where solder stencil possible desired, acceptable results obtained only applying flux pre-tinned pads. This done using non-metallic spreader applying no-clean flux paste pads board. careful scratch pads board. Apply liquid flux solder balls package. Once liquid flux applied, within minutes, place package board then reflow sure board's alignment features fudicials then place component using either mechanical manual means). Reflow solder balls using directed edge under package body. recommended that temperature experiments conducted determine optimum conditions. Remove board from heat source allow cool safe handling temperature. Inspect board package verify proper solder ball collapse observe defects that have been caused rework procedure.
14.10
14.10.1
Package Performance
Thermal Performance
general, three factors affect thermal performance BGA: package board materials, package geometry, environment. Obviously, more thermally conductive materials, better package dissipates heat. PBGA package, molding compound that surrounds chip, which provides mechanical protection well surface marking, typically 45mils thickness main barrier elimination heat from package. general design-related factors have greater thermal effect PBGA than material-related variables. large spreads heat easier, does larger package size thus higher ball count. Substrate design features have tremendous effect package's ability dissipate heat. Vertical vias running through substrate help transfer heat from solder balls. Four-layer designs often incorporate conductive 2-ounce copper ground planes, which have significant, positive effect thermal performance. Enhanced PBGA thermal balls under while H-PBGA HL-PBGA utilize heat spreader slug across package dissipate heat even more efficiently. PBGAs with center thermal balls dissipate considerable heat into board. considerable increase thermal effectiveness package obtained using boards that thermally efficient, increasing airflow, providing thermal paths from board. Remember, with PBGAs, board your primary heatsink. Environmental conditions play critical role thermal performance PBGAs. Ambient conditions, junction case temperatures, device's placement orientation board, conjunction with volume temperature flowing past unit present broad range possible thermal solutions problems packaging. Typically package cannot capable handling given power requirement unless environmental conditions allow heat dissipate. When environmental geometric constraints limit BGA's ability dissipate heat, copper aluminum heatsink often used provide additional method heat transfer. with other types packages, heatsinks BGAs vary design methods attachment. Most applications recommend maximum case temperature package. Various factors effect case temperature including ambient conditions airflow. case temperature exceeds recommended rating, heatsink required. Contact Intel applications engineer product determine heatsink been developed particular package application.
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Ball Grid Array (BGA) Packaging
Refer Chapter this handbook more information thermal characteristics.
14.10.2
Electrical Performance
Generally, fine-line laminate base lack long pins, electrical performance BGAs typically better than pinned packages. shortening electrical paths solder balls through plated via-holes conducting plane/ground plane reduces electrical parasitics. This improved further optimizing shortening overall trace length. electrical performance details package, please consult product data sheet call your local Intel sales office.
14.11
Revision History
General review edit chapter Added package proliferations Added Style, H-PBGA information
2000 Packaging Databook
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