从2003年开始做这个,什么像内存槽这样的连接器等,先是有铅,后来转到无铅.
首先,钢网开孔是个难点,你可以根据一个经验公式来计算:
H=Hole diameter
D=Lead diameter
T=Board thickness
L=Width of lead in the X direction (For square lead)
W=Width of lead in the Y direction (For square lead)
π=3.14
Hole Volume (HV)=(π)(H/2)(H/2)(T)
Lead Volume (LV)=(π)(D/2)(D/2)(T) (For round leads)
Lead Volume (LV)=(L)(W)(T) (For square or rectangular leads)
Annular Ring Area(RA)=(π)(L/2)(L/2)-(π)(H/2)(H/2)
Required solder volume (SV)=HV-LV
"Required Print Volume (PV)=(2)(SV) (50%)
<50% solder paster shrinkage factor during reflow>"
Required Print Area (PA)=(F)(PV)/stencil thickness
F=Inspection Factor
.7=no fillet
.9=fillet on both sider
0.8=fillet on primary side
1.0=large fillet on both sides
Note: Must consider the solder paster volume for annular ring.
有点需要注意,二个孔间距最好在0.3mm以上,过小的话容易出现锡丝造成短路.
因求锡理,所以对印刷机要求比较高,速度肯定不能过快,考虑会不会成为生产瓶颈.
像FUJI那种老式的印刷机,刀头上有个PUSHER,会把锡往下挤,比较适合这种工艺.
炉温也要考虑,因一般连接器吸热多,可能会导致温差过大,所以调炉温比较麻烦;
助焊剂残留,一盘在元件脚上,锡导致ICT误测增多,有点痛苦,使用氮气有所帮助;
另元件耐高温等,这是做PASTE IN HOLE最基本的条件.
忘了件事,如果孔过大,锡容易渗透过去,到时你会发现机械,炉里全是锡膏.
如有做过的朋友,多多指教一下.