Bottom side adheasive

Hi Steve,

first you have to decide if you need adhesive or you can go with solder. Usually depends on the TH parts. Otherwise dispensing is always more problematic process than print. I would go with the printer and stay away from troubles. It is faster and safer(unless you have some new top equipment like precise jet printers.....) Regards, Emil

reply »

Steve,

We use stencils for applying adhesives to PCB's, with our DEK Proflow system. Works well for us. Once in a while, we have to manually add adhesive to a specific location depending on the component height. Vary rare though. You shouldn't have this issue if your just glueing down chip components.

Stencil clean-up can sometimes be a BEE-OTCH though, according to the operators......

reply »

We exclusively use a printer to do glue these days but keep in mind there are times when glue and paste work best. Things like poor layout (ie shadowing) or tall parts that may shadow themselves or a wave solder machine that is not particularly good at doing chips, these will be soldered if you do a glue and paste. But of course for this process you need a glue dispenser too.

reply »

If you find the correct type of adhesive/needle size then dispensing certainly is no problem. With a footed needle a very repeatable process too. Much more flexible than stencil printing and no need to mess around with stencil cleaning. But with auger type equipment of course much slower than printing, especially if you have a large number of dots to dispense. If you keep your pump and needle clean there shouldn't be very many issues.

reply »

I have previously experienced dispensing glue dots using a camalot system. This was used to dispense dots for a variety of components, as the SMT was applied post through hole and then wave soldered. No paste was used in the process. The other benefits of dispensing was that the program could be easily changed to add/remove or modify dots.

I am now involved in the process of screen printing adhesive, using metal screens to apply glue for second side discrete components. The advantage of this method is that the cycle time is quicker and unaffected by the number of components. You also don't need to expand your line by adding another piece of equipment to dispense glue. However this method would require a more difficult setup for components with a higher stand off.

If no through hole components are ed and wave soldered further on in the process, then obviously doubled side reflow is preferred.

reply »

As the technology has changed towards surface mount, so has the applying adhesive. In the past clinching parts would have knocked off SMD parts, but no that has all changed. So applying the adhesive via screen print is common and any thru-hole parts are kept at a minimum or the equipment that puts them in does not damage parts.

You process and equipment will dictate you choice between the two. I have done both processes. I like screen printing adhesive because we can cut stencils to apply adhesive in areas where we always get solder shorts and it eliminates the defect. It's a nice trick for contract manufacturing as most customers will not redesign their boards.

reply »

We have been running double sided surface mount pcb assembly for several years with no adhesive needed. We paste, place and reflow one side, then repeat the process for the other side. With Rs, Cs and small to medium ICs we have no problem with parts falling off the bottom side when the pcb goes throught the oven for the second time.

In your case I am assuming you have more parts on the top side than the bottom side. I would load the bottom side with the few Rs and Cs first, then load the top side second. Unless you have very large Rs and Cs, you should not need any adhesive.

reply »