Good thorough response Adam! Thanks and Hello. (Again) Hadco Printed Circuits Tech Center Two / Watsonville _/_/_/_/_/_/_/ _/_/_/_/ _/_/_/_/_/_/ _/_/_/_/_/_/ _/_/ _/ _/_/ _/_/ _/_/ _/ _/_/ _/_/ _/_/ _/_/_/_/ _/_/_/_/_/_/ _/_/_/_/_/_/ Dave Hoover (408) 728-6677 Senior Process Engineer (408) 728-1728 Fax [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: Re: Burp Cycle! Author: [log in to unmask] at SMTPLINK-HADCO Date: 10/18/95 2:09 AM Brian, I believe you are referring to a "kiss" cycle which some shops utilize as part of their multilayer panel lamination cycle. A kiss cycle is contact pressure (usually about 50 psi) in the hot press for a set time, until "kick-over" to "high pressure" (usually 150-225 psi with vaccuum assist hydraulic presses) for the remaining time of the hot press portion of the cycle. If a "kiss" cycle is thought to be necessary, the time duration of the kiss portion of the cycle is best determined via a fluidity curve done for you by your b-stage supplier. The fluidity curve will be based upon the resin system used, and your average heat rise (measured via thermocouples) at the center and outer panel(s) in a book. The optimum kick over time ("x" minutes into the hot press cycle) will be the "between point" for the minimum viscosity curves of the center and outer panels, on the time axis of the curve. In my experience, the intention of the kiss cycle is to apply pressure when the resin, throughout the stack of panels, is in a state of flow, with the theory being that this will help to ensure complete encapsulation of all circuit features. Forcing air and volatiles from the panels is more effectively achieved with a properly charaterized press cycle, matched to the resin system. And vacuum assist is of course the ultimate addition to ensure complete evacuation of volatiles. Some Practical (I hope) Comments On Usefulness & Applicability: 1. Some of the people who have been in the industry longer than I may have further comments on this, but I believe that "way back when", when very high lamination pressures were used, and there was no (or little) vacuum assist, and most people used a steel separator between each panel, and there were heavy (and not very well controlled black oxide coatings) - a "kiss" cycle was used because there was concern that applying high pressure to the boards prior to resin flow could shear or crush the oxide growth that was supposed to enhance the bond, thus resulting in a poorer bond. 2. I believe that some resin systems are formulated, via scale flow, with the intention of having them be the best resin systems to use in processes that utilize a kiss cycle. I also believe that in todays "controlled and monitored" raw material manufacturing processes, and board fabrication proceses, that kiss cycles are often not necessary, but are more something that provides an extra level of comfort for those who use them. 3. One situation where a kiss cycle is very necessary, is when laminating with aluminum separators and using prepreg with what I have heard referred to as "resin bumps". (My experience is that resin bumps is a rare occurence - except on the resin-rich "thick plys", such as the 7628's that yield 9+ mils. In the field, I have seen quite a bit of this material with resin bumps.) In a "straight high pressure cycle", with aluminum separators, the aluminum is forced to form to the shape of these bumps prior to the resin flowing, and then when the resin flows and cures the outer surfaces of the panels can have an "orange peel" texture that is quite ugly and may impact outer layer processing. In this scenario, adding a properly characterized kiss cycle will eliminate the surface condition caused by the resin bumps, because the resin bumps will flow prior to application of high pressure. Another situation where I will recommend that customers try a kiss cycle is when they have an intolerable level of image transfer. Depending on the high pressure being used, and the copper weights on the inner layers, a kiss cycle will sometimes help to further reduce the image transfer evident on the outer layers after lamination. Sorry for the long winded answer, I hope this is helpful, Adam Davies Product Manager, CACr Lamination Foil JJA (Johnson & Johnston Associates) Office - (603) 329-5691 Voice mail - (603) 329-7215, Ext 108