surface mounting, mount designing board material selection critical. M

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surface mounting, mount designing board material selection critical. M

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SURFACE MOUNTING PROCESS PRINTED CIRCUIT BOARD DESIGN
surface mounting, mount designing board material selection critical. Mount designing influence solder yield. substrate material influence post-soldering reliability. This section discusses mount designing standards board material selection criteria.
2.2.1 MOUNT DESIGN
Fig. give recommended mount dimensions. They used standards designing. (1)TSOP Example (2)TSOP (II) Example (3)QFP Example (4)QFP Example Fig.4-1 Fig.4-2 Fig.4-3 Fig.4-4
Mar.'98
SURFACE MOUNTING PROCESS
Package outline drawing
Detail
Supplementary information
Mount dimensions definitions mount dimensions given below, along with their recommended values.
pitch should equal package lead pitch.
Recommended dimensions
0.65 0.05 0.25 0.25 0.15
Dimensions
Cleanability mounted boards Soldering strength Mask pattern accuracy visual inspection soldering Prevention solder bridges
Fig.
TSOP EXAMPLE
Mar.'98
SURFACE MOUNTING PROCESS
Package outline drawing
Detail
Mount dimensions definitions mount dimensions given below, along with their recommended values.
pitch should equal package lead pitch.
Recommended dimensions
1.27 0.05 0.25 0.65
Dimensions
Supplementary information Cleanability mounted boards Soldering strength Mask pattern accuracy visual inspection soldering Prevention solder bridges
Fig.
TSOP EXAMPLE
Mar.'98
SURFACE MOUNTING PROCESS
Package outline drawing
Mount dimensions definitions mount dimensions given below, along with their recommended values.
pitch should equal package lead pitch.
Recommended dimensions
0.65
Dimensions
Supplementary information Cleanability mounted boards Soldering strength Mask pattern accuracy visual inspection soldering Prevention solder bridges
Fig.
EXAMPLE (LEAD PITCH 0.65mm GREATER)
Mar.'98
SURFACE MOUNTING PROCESS
Package outline drawing
Mount dimensions definitions mount dimensions given below, along with their recommended values.
pitch should equal package lead pitch.
Recommended dimensions
0.25 0.15
Dimensions
Supplementary information Cleanability mounted boards Soldering strength Mask pattern accuracy visual inspection soldering Prevention solder bridges
Fig.
EXAMPLE (LEAD PITCH 0.5mm LESS)
Mar.'98
SURFACE MOUNTING PROCESS 2.2.2 PRINTED CIRCUIT BOARD MATERIAL
Boards generally divided into printed-wiring boards (printed boards) whose material epoxy resin-based, thick-film circuit boards (ceramic boards) whose material made from ceramic. Printed boards, which used popularly both household industrial applications, divided roughly into four types shown Table according purposes.
Table
Type Printed-wiring board
BOARD MATERIAL EXAMPLES
Item Resin Phenol Epoxy resin Formation Base material Conductor paper paper Copper Copper Copper Copper Copper Ag-Pd Features cost,easy mass-produce. Placed between paper phenol glass epoxy terms features. Superior insulation moisture resistance.Dimensions stable. Highly reliable with high Tg.More reasonable than glass polyimide boards. Flexible Applications Household electronic equipment (TVs,VCRs,radios) Audio equipment,VCRs,etc. Electronic equipment industrial use. (Computers,office automation equipment) Chips board(COB)thin type
Paper-and-phenol (FR-2) board Paper-and-epoxy (FR-3) board Glass epoxy (FR-4) board Heat-resistant glass epoxy board
Epoxy resin Glass fabric Heat resistant Glass fabric epoxy Polyimide Alumina ceramic
Flexible board Ceramic board
Cameras,electronic calculators,etc. Highly heat resistant conductive. Electronic components Highly reliable. automobiles
board material needs selected consideration electrical radiation characteristics. Areas discussed next page should also considered.
Fig.5
CROSS SECTION GLASS EPOXY BOARD
Mar.'98
SURFACE MOUNTING PROCESS
Prevention mound oxidization printed boards, conductors that form mount pads made from copper foil. surface mount pads rust depending storage conditions soldering temperature, possibly resulting insufficient soldering. ensure high-reliability soldering, oxidization prevention treatment shown Table given mount surface that components soldered satisfactorily.
Table Treatment Prevention Mount Surface Oxidization
Surface treatment Protective material Solder leveler treatment Solder Pre-flux Rosin-based flux Ensures good solderability. Board becomes dirty easily flux applied over. Pre-coating Alkylimidazole Formed copper surface. Ensures good solderability. Solderability become poor when devices mounted both sides.
Advantages Copper surfase expo outside. Disadvantages Solder thickness uneven solderability unstable.
preflux surface treatment recommended mount fine-pitch ICs, such TSOPs. There many kinds preflux. Select optimal according application conditions. Mount pads need surface-treated soldering when fine-pitch mounted them. this case, solder plating recommended ensure uniform solder thickness. Board warping prevent board warping after solder reflow, following countermeasures implemented: Make sure that copper conductor rate equal between front back. Provide warping prevention mechanism prevention warping during reflow (cooling). heat-resistant glass epoxy board. prevent warping, also important board appropriate type thickness. Determine them close discussion with manufacturer. Solder joint reliability ensure solder joint reliability, thermal expansion coefficient components board needs considered. When ceramic package mounted board, ceramic board recommended. thin packages (such TSOPs), silicon chip percentage high package, that virtual thermal coefficient entire package smaller. Therefore, board material needs selected carefully.
Mar.'98

surface mounting, mount designing board material selection critical. M

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