Dennis, Placement Jaws on a SMT placement machine?????? Don't remember seeing one with jaws, just a suction tip. At least not on chip shooters, maybe to place much larger parts? I thought jaws where only on PTH parts insertion systems.
I have not used supplied libraries from Protel either the few times I had on parts that I felt how bad could it be (my fault to I did not check them well enough) they burned me, not just SMT but PTH parts too, a simple TO-220 the holes where too small, never caught it till board was built. Bob Wolfe ----- Original Message ----- From: "Dennis Saputelli" <[EMAIL PROTECTED]> To: "Protel EDA Forum" <[EMAIL PROTECTED]> Sent: Monday, March 15, 2004 11:49 PM Subject: Re: [PEDA] An example why IPC footprints are often sub-optimal > this is a great picture Ian! > i totally agree with your statements here > > we have found the smaller footprints to be both more reliable > and easier to assemble > a large pad deposits more paste than a smaller pad (-duh!) > this, in excess, is one of the main causes of tombstoning > > and the huge silkscreen outline accomplishes little > except maybe it makes a tiny profit for ink vendors :) > > we have NEVER been able to use protel supplied footprints > for this reason alone > > as to maximum packing density: > isn't this a function of the placement jaws? > and isn't that a moving target? > > what are good numbers for 0603 for example? > side to side and end to end? > > i have no experience w/ SMTPlus > i assume they know what they are doing and i have heard only > good things about them > but since we can't get native protel footprints it greatly > lessens the appeal for us > > when you say wave solder > are you referring to bottom side parts which are glued and > then waved? > > regardless of the pad size and in our somewhat limited > experience with this process (glue, flip and wave) > it has been less satisfactory than a fully reflowed process > > Dennis Saputelli > > Ian Wilson wrote: > > > > One to stir up the hornets nest a little...and a little off topic maybe > > > > http://www.considered.com.au/ProtelFiles/images/Phycomp_vs_IPC.gif > > > > shows the Phycomp (the old Philips, now part of Yageo) reflow 0402 > > footprint versus the 0402 footprint from the Altium P2004 Chip Resistor > > library (in the ../Library/PCB folder) which I think is based on IPC. > > > > You can see the ridiculous difference. The one on the left is based on > > reflow with a +/-0.15 mm placement accuracy. I need maximum packing > > density - IPC in this case is not on for this application. > > > > The problem with one size fits all (and an oversize like the IPC postage > > stamp footprints) is that assemblers and others can grab onto it as a > > pseudo-standard and say "we only accept IPC footprints". Instead of > > attempting to understand the pressures on the product and adapting > > processes they simply take the easy way out. Sure, using small footprints > > may reduce yield and increase costs - in some applications this is > > appropriate. By *blind* use of overgenerous footprints I think designers > > are loosing the ability to optimise their products globally - they are > > reduced to local optimisation only. And yes, this is probably a skill that > > is developed over time and with experience - but newcomers to the industry > > should be told, in no uncertain terms, that "IPC footprints are an > > appropriate starting point and since they are designed to cope with many > > soldering processes are necessarily not optimum for any.". > > > > I am not keen on any library that thinks wave footprints are the same as > > reflow. Does SMTplus makes the distinction? > > > > Ian > > > > -- > _______________________________________________________________________ > Integrated Controls, Inc. Tel: 415-647-0480 EXT 107 > 2851 21st Street Fax: 415-647-3003 > San Francisco, CA 94110 www.integratedcontrolsinc.com > > > * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * To post a message: mailto:[EMAIL PROTECTED] * * To leave this list visit: * http://www.techservinc.com/protelusers/leave.html * * Contact the list manager: * mailto:[EMAIL PROTECTED] * * Forum Guidelines Rules: * http://www.techservinc.com/protelusers/forumrules.html * * Browse or Search previous postings: * http://www.mail-archive.com/[EMAIL PROTECTED] * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
