Adhesion of conformal coating to plastic components

We have experienced poor adhesion of acrylic conformal coating to plastic bodied IC�s. The observed symptoms of this are a blistering or lifting of the coating at the surface of the component, although peel testing has revealed that this is not always present. At this time it is believed that this poor adhesion may be a result of mold release, however several other factors, including excess thermal stressing of the coating, and inadequate coating cure, are being investigated. Of these, the largest body of evidence points to mold release. An X-ray spectroscopic analysis of the surface of the components in question has revealed the presence of elemental silicon. This silicon may be present in either a silicone or glass silica form. Discussions with the component vendor has revealed the presence of a wax based mold release in the plastic. A thorough ultra-sonic cleaning of the component with freon left a hydrocarbon residue in the freon as revealed by FTIR. Has anyone else experienced similar coating problems? Are there any solutions to problems of this nature? Currently we are investigating the use of a primer for improved adhesion, changing the type of coating used (urethane is the only other option), and cleaning the components. Has anyone had any experience with these processes? Also, are there any other companies which are successfully coating plastic components with acrylic or urethane conformal coating? Thank you, Chris Fontaine Manufacturing Engineer, Circuit Card Assembly, Sanders, a Lockheed Martin Company

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| We have experienced poor adhesion of acrylic conformal coating to plastic bodied IC�s. The observed symptoms of this are a blistering or lifting of the coating at the surface of the component, although peel testing has revealed that this is not always present. | At this time it is believed that this poor adhesion may be a result of mold release, however several other factors, including excess thermal

stressing of the coating, and inadequate coating cure, are being investigated. | Of these, the largest body of evidence points to mold release. An X-ray spectroscopic analysis of the surface of the components in question has revealed the presence of elemental silicon. This silicon may be present in either a silicone or glass silica form. Discussions with the component vendor has revealed the presence of a wax based mold release in the plastic. A thorough ultra-sonic cleaning of the component with freon left a hydrocarbon residue in the freon as revealed by FTIR. | Has anyone else experienced similar coating problems? Are there any solutions to problems of this nature? Currently we are investigating the use of a primer for improved adhesion, changing the type of coating used (urethane is the only other option), and cleaning the components. Has anyone had any experience with these processes? | Also, are there any other companies which are successfully coating plastic components with acrylic or urethane conformal coating? | Thank you, | Chris Fontaine | Manufacturing Engineer, Circuit Card Assembly, | Sanders, a Lockheed Martin Company Chris, You have done all the right things analytical. Acrylic, with or without contamination, as you know in your discipline, is very thermal sensitive. It is also very contaminate sensitive under thermal stress (cold flows). In all cases, the right environment has to be assured for it to adhere as specified. This means minimum contamination as grease, dirt, silicone, moisture, or? Then, thermal conditions must be right when everything else is. Earl Moon

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| | We have experienced poor adhesion of acrylic conformal coating to plastic bodied IC�s. The observed symptoms of this are a blistering or lifting of the coating at the surface of the component, although peel testing has revealed that this is not always present. | | At this time it is believed that this poor adhesion may be a result of mold release, however several other factors, including excess thermal

| | stressing of the coating, and inadequate coating cure, are being investigated. | | Of these, the largest body of evidence points to mold release. An X-ray spectroscopic analysis of the surface of the components in question has revealed the presence of elemental silicon. This silicon may be present in either a silicone or glass silica form. Discussions with the component vendor has revealed the presence of a wax based mold release in the plastic. A thorough ultra-sonic cleaning of the component with freon left a hydrocarbon residue in the freon as revealed by FTIR. | | Has anyone else experienced similar coating problems? Are there any solutions to problems of this nature? Currently we are investigating the use of a primer for improved adhesion, changing the type of coating used (urethane is the only other option), and cleaning the components. Has anyone had any experience with these processes? | | Also, are there any other companies which are successfully coating plastic components with acrylic or urethane conformal coating? | | Thank you, | | Chris Fontaine | | Manufacturing Engineer, Circuit Card Assembly, | | Sanders, a Lockheed Martin Company | Chris, | You have done all the right things analytical. Acrylic, with or without contamination, as you know in your discipline, is very thermal sensitive. It is also very contaminate sensitive under thermal stress (cold flows). In all cases, the right environment has to be assured for it to adhere as specified. This means minimum contamination as grease, dirt, silicone, moisture, or? Then, thermal conditions must be right when everything else is. | Earl Moon Earl, Thank you for your response to my question. From your post it is my understanding that the adhesion of acrylic conformal coat under thermal stress is contaminant sensitive, however I am unclear as to how cold flow factors in to this. Could you please clarify the relationship to cold flow phenomena and adhesion under thermal stress? Thank you again, Chris Fontaine

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| | | We have experienced poor adhesion of acrylic conformal coating to plastic bodied IC�s. The observed symptoms of this are a blistering or lifting of the coating at the surface of the component, although peel testing has revealed that this is not always present. | | | At this time it is believed that this poor adhesion may be a result of mold release, however several other factors, including excess thermal | | | | | stressing of the coating, and inadequate coating cure, are being investigated. | | | Of these, the largest body of evidence points to mold release. An X-ray spectroscopic analysis of the surface of the components in question has revealed the presence of elemental silicon. This silicon may be present in either a silicone or glass silica form. Discussions with the component vendor has revealed the presence of a wax based mold release in the plastic. A thorough ultra-sonic cleaning of the component with freon left a hydrocarbon residue in the freon as revealed by FTIR. | | | Has anyone else experienced similar coating problems? Are there any solutions to problems of this nature? Currently we are investigating the use of a primer for improved adhesion, changing the type of coating used (urethane is the only other option), and cleaning the components. Has anyone had any experience with these processes? | | | Also, are there any other companies which are successfully coating plastic components with acrylic or urethane conformal coating? | | | Thank you, | | | Chris Fontaine | | | Manufacturing Engineer, Circuit Card Assembly, | | | Sanders, a Lockheed Martin Company | | Chris, | | You have done all the right things analytical. Acrylic, with or without contamination, as you know in your discipline, is very thermal sensitive. It is also very contaminate sensitive under thermal stress (cold flows). In all cases, the right environment has to be assured for it to adhere as specified. This means minimum contamination as grease, dirt, silicone, moisture, or? Then, thermal conditions must be right when everything else is. | | Earl Moon | Earl, | Thank you for your response to my question. From your post it is my understanding that the adhesion of acrylic conformal coat under thermal stress is contaminant sensitive, however I am unclear as to how cold flow factors in to this. Could you please clarify the relationship to cold flow phenomena and adhesion under thermal stress? | Thank you again, | Chris Fontaine Chris, First, acrylic "moves" (cold flows) over any surface, or not, be it fluid or solid. It does not bond to anything readily, if at all. If contaminates of any type are under its placement, it further resists "bonding" and "delaminates" or does not adequately "bond." Please understand, as I know you must, at your level of technical expertise and with your history of process capabilities, acrylic is both thermal (not so much pressure sensitive) and contaminate sensitive. It neither likes to bond to anything (period) and, especially does not like to "bond" when contamination found under its application. You folks (Sanders - must have a huge history) have known this for years in flex and rigid/flex designs. You were one of the pioneers we all look to for this type information. Earl Moon

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| We have experienced poor adhesion of acrylic conformal coating to plastic bodied IC�s. The observed symptoms of this are a blistering or lifting of the coating at the surface of the component, although peel testing has revealed that this is not always present. | Has anyone else experienced similar coating problems? Are there any solutions to problems of this nature? Currently we are investigating the use of a primer for improved adhesion, changing the type of coating used (urethane is the only other option), and cleaning the components. Has anyone had any experience with these processes? | Also, are there any other companies which are successfully coating plastic components with acrylic or urethane conformal coating? | Thank you, | Chris Fontaine | Manufacturing Engineer, Circuit Card Assembly, | Sanders, a Lockheed Martin Company Yes, we are successfully coating plastic parts. The problem described here is common (search the 1996 Technet archives and you'll find quite a thread on the subject) not only in conformal coating but also in printing and painting on plastic parts. It may well be that the parts are contaminated with a release agent, but more probably this is a function of the surface energy of the plastic. The way they solve this problem when printing the surface of ICs is to pass the chip through a flame. This crazes the surface of the plastic and allows it to accept ink. Similar results can be acheived through exposure to strong solvents. More practically, try using a different coating. In my experience, Dexter Hysol PC18 and Humiseal 1A20 especially are excellent for coating such parts. The Conap seems much less so. Feel free to contact me off-line for more info. Mike Moninger Thermospray Company, Inc. 1-800-952-5838

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| We have experienced poor adhesion of acrylic conformal coating to plastic bodied IC�s. The observed symptoms of this are a blistering or lifting of the coating at the surface of the component, although peel testing has revealed that this is not always present. | At this time it is believed that this poor adhesion may be a result of mold release, however several other factors, including excess thermal stressing of the coating, and inadequate coating cure, are being investigated. | Of these, the largest body of evidence points to mold release. An X-ray spectroscopic analysis of the surface of the components in question has revealed the presence of elemental silicon. This silicon may be present in either a silicone or glass silica form. Discussions with the component vendor has revealed the presence of a wax based mold release in the plastic. A thorough ultra-sonic cleaning of the component with freon left a hydrocarbon residue in the freon as revealed by FTIR. | Has anyone else experienced similar coating problems? Are there any solutions to problems of this nature? Currently we are investigating the use of a primer for improved adhesion, changing the type of coating used (urethane is the only other option), and cleaning the components. Has anyone had any experience with these processes? | Also, are there any other companies which are successfully coating plastic components with acrylic or urethane conformal coating? | Thank you, | Chris Fontaine | Manufacturing Engineer, Circuit Card Assembly, | Sanders, a Lockheed Martin Company Chris, We have been experiencing the same problems, with our Urethane coating materials. We spent several months working on fixes, ranging from solvents to primers. We found that the primers do allow a complete coverage of the devices with the coating material, but the adhesion of the coating/primer mix to the device was still a problem. We have been able to get all of our Military customers to convert their specifications to ANSI/J-STD-001. If you take a look at paragraph 10.1.2.2 of the specification, (coating coverage), the requirement is to be free of voids, bubbles or foriegn material which exposes component CONDUCTORS, printed wiring conductors, etc. We have been able to get our customers to agree that dewetting on the tops of the components does not violate these requirements, and therefore does not need to be reworked. In getting this agreement with our customers, we were able to eliminate all of the 'special processing' techniques utilized to get the coating to adhere, therefore reducing the product costs. Tom Tellinghuisen Raytheon Systems Company

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| | We have experienced poor adhesion of acrylic conformal coating to plastic bodied IC�s. The observed symptoms of this are a blistering or lifting of the coating at the surface of the component, although peel testing has revealed that this is not always present. | | At this time it is believed that this poor adhesion may be a result of mold release, however several other factors, including excess thermal stressing of the coating, and inadequate coating cure, are being investigated. | | Of these, the largest body of evidence points to mold release. An X-ray spectroscopic analysis of the surface of the components in question has revealed the presence of elemental silicon. This silicon may be present in either a silicone or glass silica form. Discussions with the component vendor has revealed the presence of a wax based mold release in the plastic. A thorough ultra-sonic cleaning of the component with freon left a hydrocarbon residue in the freon as revealed by FTIR. | | Has anyone else experienced similar coating problems? Are there any solutions to problems of this nature? Currently we are investigating the use of a primer for improved adhesion, changing the type of coating used (urethane is the only other option), and cleaning the components. Has anyone had any experience with these processes? | | Also, are there any other companies which are successfully coating plastic components with acrylic or urethane conformal coating? | | Thank you, | | Chris Fontaine | | Manufacturing Engineer, Circuit Card Assembly, | | Sanders, a Lockheed Martin Company | Chris, | We have been experiencing the same problems, with our Urethane coating materials. We spent several months working on fixes, ranging from | solvents to primers. We found that the primers do allow a complete coverage of the devices with the coating material, but the adhesion of | the coating/primer mix to the device was still a problem. We have been able to get all of our Military customers to convert their | specifications to ANSI/J-STD-001. If you take a look at paragraph 10.1.2.2 of the specification, (coating coverage), the requirement is to | be free of voids, bubbles or foriegn material which exposes component CONDUCTORS, printed wiring conductors, etc. We have been able to get | our customers to agree that dewetting on the tops of the components does not violate these requirements, and therefore does not need to be | reworked. In getting this agreement with our customers, we were able to eliminate all of the 'special processing' techniques utilized to get | the coating to adhere, therefore reducing the product costs. | Tom Tellinghuisen | Raytheon Systems Company | Chris & Tom, We too have had similar problems with Urethane coating adhesion to the top of ICs, and as Tom mentions, asked ourselves "what's the requirement?" The requirement is for the pwb, conductors and solder joints to be coated, not the tops of the components. We no longer envoke 'special processing' (rework) to touch up lifting coating from IC tops. Greg Curler BFGoodrich Aerospace

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