INTRODUCTION
Wave and SMT pallets are an esntial and cost effective tool for the PCB asmbly process. Pallets designs allow for incread through put, the curing / aligning of critical components and allow for soldering of thru-hole components affected by bottom side SMT component layout violations. Review your process using the justification ction below and e how Wave and SMT pallets can improve your process.
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MATERIALS
Materials now have been designed for the wave solder and reflow PCB asmbly process. Durapol, Durostone and Haysite have been adopted and are now the materials of choice. For the lead free wave solder and reflow process Durapol and Durostone have new formulation to withstand the higher temper
ature requirement and the more aggressive fluxes. All the materials are similar in their machining and durability characteristics.
JUSTIFICATION
As a result of the newer materials, one-piece construction, and ea of machining, reduced fabrication cost, justification can be easily achieved. Listed below are some of the more notable cost reductions associated with solder pallets.
•Elimination of SMT bottom side Glue process
•Reduced 2nd hand load components due to outer edge board overlap.
惨是什么意思▫onetime pallet cost versus recurring breakaway tab cost
▫1st hand load labor versus 2nd hand load labor
•Eliminate hand masking and Kapton tape process
书房榻榻米▫fixture will mask areas on bottom side
•Eliminate recurring breakaway tab cost for odd shaped PCB’s
▫one time pallet cost
•Reduced rework / touchup cost
▫layout violation and mis-orientation of SMT components well be masked from wave
▫additional support for asmblies with heavy component and PCBs with large width dimensions
▫Better quality than hand soldering
▫Secure and alignment of critical components with over head tooling
•Increa PCB through put with multi-up pallet design
▫Allows the processing of multiple PCBs at one time.红油的做法与配方调料
▫Eliminates the additional cost of panel up layouts.
引体向上
All the above cost reductions can easily be attained with high runner asmblies. When asmblies are small runners, rework or touchup, breakaway tabs and hand masking, if applicable, can constitute justifiable paybacks.
WAVE SOLDER PALLETS
• 45° Beveled leading and trailing edges
• Aluminum stiffeners / solder dams on all four (4) sides of pallet
• Spring loaded rotary hold down buttons, made from static dissipative, high temp. plastic • Fabrication process insures flatness held within .010 over 6 linear inches
• Rail fingers .150” wide top, .250” wide bottom, and bottom edge flush with PCB bottom side • Boar
d pocket lip shall be minimum .062 standard • Board pocket shall be .030” larger than PCB in each axes • Pallet machined for solder openings, with 60° bottom side chamfers • Pallet design optimized to travel with the short axis leading/trailing
(unless PTH components layout dictates other) • PCB pocket depth will match pallet’s conveyor rails
• All fasteners mounted metal to metal with 316 SS hardware on solder side
SELECTIVE WAVE SOLDER PALLETS
• “Seal” walls can be .030” thick (min.), bad upon length • .020” clearance between the SMT components and pallet floor • Pallet “floor” shall be .030” thick (min.), ba upon size of area
• .020” min. clearance between the SMT component pad and the outside al walls (short axis only)
• .050” (lead solder) .100” (lead free solder) min. clearance between annular ring of PTH and al walls • Board pocket shall be .030” larger than PCB in both axes
服装广告词吸引人• Pressure relieving pallet solder side, shall be applied to meet aspect ratio requirements • Aluminu
m stiffeners / solder dams on all four (4) sides of pallet
• Pallet conveyor edges shall be .150” wide top and .250” wide bottom, .090 min. thickness • Pallet design optimized to travel with the short axis leading/trailing (unless PTH components layout dictates other) • PCB pocket depth will match pallet’s conveyor rails
• Spring loaded rotary hold-downs buttons, made from static dissipative, high temperature plastic • 45° beveled leading and trailing edges
• Fabrication process insures flatness held to within .010” over six (6) linear inches
COMPOSITE SELECTIVE WAVE SOLDER DRAWINGS
PCB LAYOUT GUIDE LINES
PTH COMPONENT CLEARANCES FOR LEADED AND LEAD FREE SOLDER
Recommended minimum distance, from the outside edge of the annual ring to a SMT component pad:
Short axis of SMT pad layout (e figure 3-1) Long axis of SMT pad layout (e figure 3-2)
射手座双鱼座
SMT COMPONENT HEIGHT CLEARANCES
嗳气的原因Offt tall SMT components as much as possible to insure the maximum aspect ratio and
pressure relieving (e figure 3-3).
PTH COMPONENT PCB PLACEMENTS
PTH component layouts
• Align so the long axis is traveling perpendicular to the solder wave. Long axis of the PCB
travels parallel to wave solder conveyor.
• If PTH connector placement is required along outside edges of PCB, leave sufficient spacing
for al wall support between components. • Group PTH components to allow for larger solder openings. This will allow better bottom
side preheat penetration to insure: o good topside solder fillets
o reduced occurrences of upward PCB bowing due to insufficient bottom side preheating (if topside preheat is ud)
• Do not place passive SMD components within PTH component land patterns
