New adhesives: for Iow-temp cure without trade-offs and ultra high-speed dispensing

Citation

(2000), "New adhesives: for Iow-temp cure without trade-offs and ultra high-speed dispensing", Soldering & Surface Mount Technology, Vol. 12 No. 1. https://doi.org/10.1108/ssmt.2000.21912aad.010

New adhesives: for Iow-temp cure without trade-offs and ultra high-speed dispensing

New adhesives: for Iow-temp cure without trade-offs and ultra high-speed dispensing

Keywords: Loctite, Adhesives, Surface mount assembly

Fast, safe bonding of heat-sensitive components - without compromising strength or application - and ultra-high speed dispensing, are now possible with new Loctite surface mount adhesives (SMA).

Plate 6Loctite Chipbonder® SMA 3619 was specifically developed to bond high sensitive components

The first of these new additions to the Chipbonder® SMA range (Plate 6) are 3619 and 3620 (which differ only in their recognition colour - red or yellow) were specifically developed to bond high sensitive components (e.g. LED) which could be damaged by the industry-norm cure-temperature of 125°C. They embody an innovative, patented low temperature technology which imparts two major benefits:

1. 1.

   full 100 percent cure at temperatures as low as 80°C; and

2. 2.

   a shorter oven time to achieve full cure.

Their recommended cure profile is only 90 seconds at 100°C - compared with two to three minutes at 125°C when ordinary SMA are used.

The reduced exposure of heat-sensitive components to prolonged oven-curing temperatures, say Loctite, will cut component failure rates. This means that re-work will be greatly reduced, process efficiency will be improved - and manufacturers will save money.

These faster times do not demand trade-offs in bond strengths and dispensing speed. Both 3619 and 3620 have typical pull-off and torque strengths (according to IPC SM817 tests, using C-1206 on bare FR4 boards) of 50N and 50N.mm respectively - which are comparable to strengths of SMAs cured at higher temperature profiles between 125 and 150°C.

Loctite's latest low-temperature curing SMAs were the direct result of approaches from board assemblers wishing to use heat sensitive components and protect visible function indicators from thermal stress. Similarly, close liaison with major international equipment manufacturers resulted in the development of another two new Chipbonders: 3621 (red) and 3622 (yellow).

High speed dispensing

Chipbonders 3621/3622 boost application speeds to a previously commercially-unattainable high; they can be dispensed by both pressure-time and positive displacement dispensing equipment at speeds in excess of 46,000 adhesive dots/hour. During tests an 0.632mm diameter dot was dispensed by a Universal GDM machine at 46,000 dots/hour. Even a 1.058mm dot was still dispensed at 41,000 dots/hour. The specified dot profile was consistently maintained and placed without stringing. The maximum possible dispense speed of 46,000 dots/hour was also achieved with Fuji GL 541 E equipment during similar tests.

Loctite 3619/3620 and 3621/3622 are one-part epoxy adhesives that exhibit excellent drop shape control, good dot profile and good on-board electrical properties. They have high "wet" or "green" strength to withstand acceleration and deceleration during production transport, and have passed the PC SM817 (2..4.42.1) hot solder dip test. Supplied in a variety of bubble-free ready-to-use syringes, they have a minimum shelf-life of six months stored at 8°C.

With these new SMAs Loctite offers a complete range of chipbonders for different requirements with regard to product application and product properties. Whether the customer wants to use syringe dispensing, pin transfer or stencil printing - Loctite has a solution. Whether the customer wants to have a peaky or a flat dot profile, an exceptionally high humidity resistance or a faster curing cycle - Loctite has a solution. All SMAs are available throughout Europe from local sources.