loctite乐泰焊锡膏技术培训最新完整版本.ppt

**7370**7671**7772**8676**8777**1211**13**18**19**2834**3844**Comparingdirectlytosqueegees.....Theforcesinvolvedinscreenprintingareinfluencedbyanumberofinteractingparameters,whicheffectivelymeanswehaveverylittlecontroloverthe“critical”transferforces.**Comparingdirectlytosqueegees.....Theforcesinvolvedinscreenprintingareinfluencedbyanumberofinteractingparameters,whicheffectivelymeanswehaveverylittlecontroloverthe“critical”transferforces.**Comparingdirectlytosqueegees.....Theforcesinvolvedinscreenprintingareinfluencedbyanumberofinteractingparameters,whicheffectivelymeanswehaveverylittlecontroloverthe“critical”transferforces.**54**Squeegeescanbemetalorpolyurethane,accordingtotaste.Polyurethaneoffersthechancetocontrolprintheightbychangingpressureandmetalworkswellonacorrectlychosenstencilbecauseitisveryinsensitivetopressurechanges.Ineithercase,theywillwearand/orbecomedamagedandsorequireroutinereplacement.**5151**4852**4953********5857****6159**6260**6361**Midchipballsarecausedbyplacingachipcomponentwithtoomuchforceontotoomuchsolderpaste.Pastesquirtsunderthechip,isreflowed,meltsintoonelargeballthatpopsouttooneside.Theyhaveprobablyalwaysbeentherebutonlybecameobviouswithno-cleanprocesses**6563**“Homeplate”designsandothermodifiedshapescanbeusedtoeliminatesquirt-outs,eitherbyremovingpastefromthedangerareaorbysimplyreducingthepastevolume.ForICsandotherlandrows,ignorelandsizeandmakeaperturewidthequaltohalfthepitch.The“standard10-20%reduction”wouldprintsomuchpasteonwidelandsthatbridgingwouldprobablyoccurormaketheaperturesonarrowfornarrowlandsthatpastewouldblockintheapertures.**6664**6967**7068**676