Ds as w 00335427

Confidential

Jon S. ProkopVice President, Manufacturing

(972) [email protected]

Assembling SRD Products Onto Assembling SRD Products Onto

Customers’ Customers’ PWBsPWBs

Confidential

• Considerations/Topics– PWB footprint (layout)– Solder mask use/layout– Type of solder– Temperature profile– Type of soldering equipment– Stencil– Flux– Cleanup– Standards

Assembling SRD Products Onto Assembling SRD Products Onto

Customers’ Customers’ PWBsPWBs

Confidential

PWB Footprint/LayoutPWB Footprint/Layout

• Depending on which reference manual you use, or internal process preferences, the PWB footprint will be:– the same size as the part solder pad layout, or– slightly larger for each feature (typical).

• We chose to make the PWB footprint for each package slightly larger– SM20H: Pads are 0.005” wider and 0.020” longer than those on the

package– SM20L: Pads are 0.005” wider and 0.025” longer than those on the

package• Allows for some misalignment during part placement• Solder flow is visible - No castellations on these parts.

Confidential

Footprint ComparisonFootprint Comparison

SM20H

Dimensions in inches (mm).

.09 (2.286)

.370 (9.398)

0.0000.00

0

.065 (1.651)

.105 (2.667)

.145 (3.683)

.185 (4.699)

.225 (5.715)

.265 (6.731)

.305 (7.747)

.345 (8.763)

.090

(2.2

86)

.43511.049

.122

5 (3

.115

)

.162

5 (4

.127

5).1

475

(3.7

465)

.187

5 (4

.762

5)

.220

(5.5

88)

.310

(7.8

74)

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0.0000.00

0

.140

(3.5

56)

.270

(6.8

58)

.410

(10.

414)

.0775 (1.9685)

.1025 (2.6035)

.1175 (2.9845)

.1575 (4.0005)

.1975 (5.0165)

.2375 (6.0325)

.2775 (7.0485)

.3175 (8.0645)

.3575 (9.0805)

.3825 (9.7155)

.4600

.197

5 (5

.016

5).1

725

(4.3

815)

.212

5 (5

.397

5).2

375

(6.0

325)

Dimensions in inches, (mm)

SM20L

(11.684)

Footprint ComparisonFootprint Comparison

Confidential

CastellationsCastellations• These parts/packages do not have castellations

– Castellations are expensive (NRE & recurring cost)– The contribute to distortions of the substrate which can

complicate assembly (lower yield)– Customers want lower cost products

• Customers like castellations– They can see a solder fillet - visual inspection

• Castellations are allowable by industry specifications– IPC-A-610 allows & specifies a minimum of 25% solder flow

up into the castellations, if they are present (Section 10.2.4, paragraph 6)

– IPC refers questioners to Section 10.2.1, “Chip Component/ Bottom Only Terminations” for parts without castellations.

– IPC plans a revision which will specifically address non-castellated parts sometime in the next three years

Confidential

Solder MaskSolder Mask

• Depending on which reference manual you use, or internal process preferences, the Solder Mask footprint will be:– the same size as the PWB solder pad layout, or– slightly larger for each feature – slightly smaller for each feature

• We chose to make the solder mask openings the same size as the PWB pads

Confidential

SolderSolder

• Single or two-sided assembly?– Two sided typically requires a higher melting point solder

for one side of the assembly

• Form– Typically a screenable paste consisting of very small solder

particles suspended in flux

• Metal content– The amount of solder metal in pastes is specified as “%

solids” or “% metal”– Metal content is a determiner of the final thickness of the

soldered joint– “Thicker is better”

Confidential

• We use SN62 (Federal Spec. QQ-S-571F)– Approximate composition = 62%Sn/36%Pb/2%Ag– Liquidus (melting point) = 189°C– Solidus (freezing point) = 176°C– 80% metal content– RMA flux

• Why? Because that’s what we have onBecause that’s what we have on--handhand.• Other popular solders

– SN63; eutectic at 183°C– SN60; non-eutectic; liquidus = 190°C; solidus = 182°C

• Choice of solder influences soldering profile

Type of SolderType of Solder

} A non-eutecticsolder

Confidential

Soldering ProfileSoldering Profile

• Two Classic Profiles:– Ramp & hold– Triangular

• Exact profile depends on the equipment used– Never exactly duplicated

• Most popular types of equipment are:– Convection (U.S. typically)– IR (Europe & Asia)

Confidential

Ideal Ideal ReflowReflow Soldering Profile for SN63 (Not SAC) SolderSoldering Profile for SN63 (Not SAC) Solder(Ramp & Hold)(Ramp & Hold)

50

100

150

200

250

0

1 2 3 4 5 6

Time (minutes)

Tem

per

atu

re (

°C) Liquidus - 183°C

Peak Temperature = 210°C - 235°C

Pre-Drying = 120°C - 150°C

Time above Liquidus ~ 30 sec.

Confidential

Reflow Soldering Profile for SN63 (Not SAC) Solder(Triangular)(Triangular)

50

100

150

200

250

0

1 2 3 4 5 6

Time (minutes)

Tem

per

atu

re (





Confidential

Profile We Used for SN62 (Not SAC) SolderProfile We Used for SN62 (Not SAC) Solder

50

100

150

200

250

0

1 2 3 4 5 6

Time (minutes)

Tem

per

atu

re (





Confidential

ReflowReflow Soldering EquipmentSoldering Equipment

• Vapor Phase - Environmental concerns• Wave - Won’t typically be used with our products• IR - Widely used in Europe and Asia• Convection - Recommended

Confidential

• IR systems depend on radiated energy to heat joints to soldering temperatures

• Wavelength/spectra of the energy radiated varies with system brand and age

• Wavelength absorbed by each component varies– Metals typically absorb in the near-IR region– Organics (plastics) & oxides (ceramics) typically transparent

in near-IR, but absorb middle- and far-IR to varying degrees– Thus, one can “burn up” one component while soldering

another


Confidential

• Convection systems avoid problems of IR systems while offering similar high throughput, reliable soldering

• We used a Heller, model 1700 to solder the TR products to the DR boards


Confidential

FluxFlux

• Many different flux types are available– QQ-S-571 designators are still used to identify fluxes (RMA,

WSF-O, WSF-1, LR)• Water soluble and “No Clean” (LR) fluxes are increasingly

popular

– ANSI J-STD-004 reclassified fluxes according to activity• L0 = Some RMA, some LR• L1 = Most RMA• M0 = Some LR• 33 = Some water soluble• H1 = Most water soluble

Confidential

Stencil/ScreenStencil/Screen

• Stencils are preferred by most assemblers– Better solder joint thickness control

• A Stencil is a thin sheet of metal with openings corresponding to where the solder joints are to be made– The openings in the stencil can be made the same size as the

PWB solder pads, or slightly smaller or larger

• We made the openings in our stencil the same size as the PWB solder pads

Confidential

Solder Joint ThicknessSolder Joint Thickness

• Determined by “% Metal,” solder mask openings, Stencil openings, thickness of solder plating on the PWB and Stencil thickness

• In our case for the TR1000, (80% metal, Stencil = PWB pads, Solder Mask = PWB pads, PWB pads larger by 60% than part pads, and solder plating on PWB– Solder joints will be 0.002” to 0.003” thick

Wt% Vol%Metal Metal75 24.3280 30.0085 37.7890 49.1095 67.06

Confidential

CleaningCleaning

• “To Clean or Not To Clean, That Is the Question”– The move is on to “No-Clean” fluxes

• With any other type of flux, cleaning after assembly is very important– Long Term Reliability

• Height of the component above the PWB (as determined by solder joint height) and the spray pressure, fluid volume and solvent type (probably water) are keys to producing properly cleaned assemblies

• Poorly cleaned PWBs– Shorts/Signal Loss– Residue/Contamination

Confidential

ReferencesReferences

• Modern Solder Technology for Competitive Electronics Manufacturing - Jennie S. Hwang, PhD; McGraw-Hill

• Soldering Handbook for Printed Circuits and Surface Mounting - Howard H. Manko; Van Nostrand Reinhold

• Design Guidelines for Surface Mount Technology - Vern Solberg; Tab Books

• Surface Mount Technology for PC Board Design - James K. Holloman. Jr.; Howard W. Sams & Company

• Surface Mount Land Patterns (Configurations and Design Rules) - ANSI/IPC-SM-782

• Surface Mount & Mixed Technology PCB Design Guidelines - David Boswell; Technical Reference Publications Limited

Confidential

Applicable StandardsApplicable Standards

• ANSI/IPC-A-610 - Acceptablity of of Electronic Assemblies• QQ-S-571F - Federal Specification, Solder, Electronic (96 to 485°C)• ANSI/J-STD-001 - Requirements for Soldered Electrical and Electronic

Assemblies• ANSI/J-STD-002 - Solderability Tests for Components, Leads,

Terminations, Lugs, Terminals and Wires.• ANSI/J-STD-003 - Solderability Tests for Printed Circuit Boards• ANSI/J-STD-004 - Requirements for Soldering Fluxes• ANSI/J-STD-005 - Requirements and Test Methods for Solder Paste• IPC-TM-650 - Test Methods Manual• IEC-1191-1 - Generic Standard, Requirements for Soldered Electrical and

Electronic Assemblies Using Surface Mount and Related Assembly Technology

• ISO-9453-1990 - Soft Solder Alloys -- Chemical Compositions and Forms

Confidential

Comprehensive TestComprehensive TestOn Presented MaterialOn Presented Material

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