Though still looking for an alternative test method and acceptance/rejection criteria to determine more accurately voiding in adhesives, I now need to get a refresher on the adhesive application process. I?m looking both at epoxies and films. I am first looking at two part epoxies, that are thermally conductive, to bond RF amps to a cold wall. There are many and suggestions are appreciated. The process itself, using these epoxies, is pretty straightforward as I see and have experienced it, but I am seeking process improvement suggestions. Believing it is true that two part types promote an exothermic reaction, is it not true that much voiding is prevented if most of the outgassing is effected just by letting "nature" take its course? This is provided, of course, the bonding surface areas are small enough, well cleaned, and the process is well managed. In a well managed process, isn?t application the primary factor promoting a void free bond? This is true, if both surfaces are well ?coated? during the process whether using syringes or screens/stencils (I?m looking at this much the same way as in SMT and hybrid circuit assembly). Using a film type adhesive, the bonding process takes place as an endothermic reaction. I relate this to using prepregs, as in rigid MLB?s, or acrylics, as in flex circuitry, with bonding taking place in a lamination press under temperature and pressure over time. I haven?t quite figured out how to use this process, if practical, on parts being bonded to the cold wall inside a box about two inches on a side. Here, I?m thinking of small clamps used to pressure the part to the wall. I?m also thinking of managing this process inside an autoclave, or ?turkey? bag, with many bondings being effected simultaneously, while applying heat and pressure over time while pulling enough vacuum to get the gas out and minimize voiding. Any thoughts here much appreciated as well. I?m also thinking of using the autoclave/turkey bag thing with the two part epoxies to aid in outgassing and void minimization. Wouldn?t this be much like potted or molded assembly? My biggest concern for the two part system is squeeze out and the amount pushed outside the bonding area. Any suggestions about minimizing this also greatly appreciated as well. I think the experiment here is to measure the amount as a result of the amount of adhesive placed and where. Do I need to be concerned with determining a ?low pressure? area, its shape, and how it moves under pressure? Again, I must come up with a process, hopefully not too far outside the realms indicated above, that promotes, rather than inhibits, thermal conductivity. First, it has to work thermally. Second, it has to be consistent as a process and a product. Third, because of second, quality must be verifiable and must be capable of being correlated to the process. Fourth, third means there must be a good way to measure voiding. Fifth, an experiment must be run to ensure the amount voiding correlates directly to thermal effectiveness and efficiency. Fifth is the easy part. I?m throwing a lot of stuff out to you folks, from my perspective and off the top of my head, but I know many of you have already solved these problems. Sure would like to benefit from your experiences and knowledge. Earl --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------