Steve, Not to be a nay-sayer, but I echo much of what Richard is getting at. Have used conductive and non-conductive adhesives within hermetic packages for many years. Still have items constructed this way orbiting in the Saturnian system - Cassini. Rework generally is easy, just heat the item up to the glass transition temp [can be anywhere from 40-50°C for low-class adhesives to 125-185°C for the better, more thermally stable materials]. Hot air is typically used for localized heating with mechanical removal of the offensive component. Standard equipment exists for this. It is really quite easy. Does involve operator intensive mechanical clean-up or the area to remove old adhesive. Far easier than the mess of solder and flux, etc. Many, but not all, conductive adhesives form reliable and electrically stable bonds that hold up quite well in a hermetic environment. This is NOT so, in the oxidizing, humid environment of a PWB assy. Contact resistance typically climbs quickly. If your application is only driven by voltage, instead of current, you may get away with it longer. However, always be on the alert for electromigration... As someone said, they are significantly weaker than solder - and it can get worse with age, thermal cycling, CTE mis-match, etc. Adhesives do not allow for self-centering of components although accurate dispensing of adhesive has been done for many, many years. For example, generic jelly-bean LED die are frequently on the order of 100µm square [4 mils]. Depending upon the particular device construction, sometimes side fillets are not allowed [shorts out the junction on bottom junction devices]. While dispensing 50-75µm dots is not trivial, it is done by many. There are also some materials used for jetting of conductive inks, but they typically have a great deal of solvents employed and never tested to be stable in the microelectronics application. There are many 0402 case size [and smaller] chip caps and resistors attached using Ag-filled adhesives in high-rel Mil and Implantable medical applications. Needless to say, dispense volume and pattern is important, but readily do-able. Microelectronics applications also typically deal with dispense and component placement accuracies of 12-25µm, so if one gets the correct amount in the correct location, all is typically well. In Microelectronics applications, one would never attempt to bond to a solder-coated, component. Suitable chip components typically have Pd-Ag, or straight Ag termination metallizations. Au or bare Si are other typical component terminations. Curing of the 'better/more thermally stable' adhesives generically takes place in the 150-165° range. I refer to it as attempting to adhere to a moving surface when attempting this cure to a solder coated surface - even more so when dealing with non-eutectic alloys. Yes, the solder replacement adhesives have lower cure temps than 150-165°C. Some are RT cure, UV, or in the 50°C and up range. Just remember that the glass transition temp [Tg] of the adhesive generally can only approach the cure temp [with certain exceptions]. Therefore, it would be prudent to have a very benign use temperature envelope as well. I would not adverse to listening, reading, and evaluating samples if time permits, but the real reason they are not being used in the PWB industry is because they just are not as reliable... IMHO Steve Creswick Sr Associate - Balanced Enterprise Solutions http://www.linkedin.com/in/stevencreswick 616 834 1883 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D. Sent: Monday, March 12, 2012 12:14 PM To: [log in to unmask] Subject: Re: [TN] Assembling with conductive adhesive You also need to understand the long-term reliability characteristics of silver-filled epoxy, with your design. It does not usually last as long as solder, especially not under severe thermal cycling. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo Sent: Monday, March 12, 2012 10:52 AM To: [log in to unmask] Subject: Re: [TN] Assembling with conductive adhesive (1) you need excellent pick and place machine (no self centering surface tension to help you). (2) you need to pick a good vendor with high quality silver loading (higher silver = good conductivity but poor adhesion). Few of them can do it properly. (3) you need good interface bonding with close contact of silver flakes during the life of the product. Not all of paste can do that (changes conductivity as time goes by) (4) you need components termination that can be bonded to adhesive, not all vendor supply that part or have that options. (5) you need good dispensing machine or pad printing machine. Not everybody who get use to stencil would want to (high resistance implementation). Unless you want to use ACF (capital equipment cost). (6) if you can overcome above 1-5, very nice to use the conductive adhesive. Joyce Koo Materials Researcher - Materials Interconnect Lab Research In Motion Limited Office: (519) 888-7465 79945 Mobile: (226) 220-4760 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory Sent: Monday, March 12, 2012 11:39 AM To: [log in to unmask] Subject: [TN] Assembling with conductive adhesive Hey all, Wish I hadn't lost that hour of sleep this weekend, I'll try to find it tonight. :o) Anyways, have any of you thought of trying to replace solder with a conductive adhesive for PCB assembly? There's a few out there (Henkel, Cookson, Ellsworth, etc.) that are touting them as solder replacements. When I read the technical datasheets, I'm thinking to myself, why isn't this stuff more widely used? There must be a reason. I do know it's pretty expensive almost all of them are silver filled, and I have read that the mechanical strength and thermal conductivity is not as good as solder, but what other reasons are out there not to use it? Steve ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ --------------------------------------------------------------------- This transmission (including any attachments) may contain confidential information, privileged material (including material protected by the solicitor-client or other applicable privileges), or constitute non-public information. Any use of this information by anyone other than the intended recipient is prohibited. If you have received this transmission in error, please immediately reply to the sender and delete this information from your system. Use, dissemination, distribution, or reproduction of this transmission by unintended recipients is not authorized and may be unlawful. ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________