Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Wavesoldering

Sal

#2691

Wavesoldering | 21 October, 2000

A question for all you wavesoldering buffs out there ? What i'd like to know is what causes the bulb-shape type joints around chip components when flowed over the wave ? which wavesoldering process parameter contributes to this type of defect & how can this be rectified ?

Adam

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Aaron

#2692

Re: Wavesoldering | 21 October, 2000

It sounds like the temperature of wave is a little lower. It should be 245~250 deg.C for solder Sn63/Pb37.

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Aoki Laboratories Ltd.

#2693

Re: Wavesoldering | 22 October, 2000

This may be the "wetting" problem! Assuming your process parameters are normal (work OK before), the possible reasons: 1. Presence of impurity in the solder; 2. Other impurity (oil or anti-dross) on the surface of the pot; 3. Weak solderability, due to poor flux performance. You need to tackle your problem, one by one.

David

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#2694

Re: Wavesoldering | 23 October, 2000

Unlike components where the solder paste has been reflow soldered, wave soldered components have an "infinite" amount of solder available to make a solder connection.

If you have good solder flow, pad and component termination size are going to be big drivers in the amount of solder that remains on a termination after wave soldering.

Continuing, bilbous solder connections are less reliable than those with contact angles of LT 90�

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JohnW

#2695

Re: Wavesoldering | 24 October, 2000

Adam,

Did some work on this a bit back via some good old Taguchi DOE and like Dave(the guru)F say's your component terminations is a big factor but I also foundthat the amount of flux you put on as well as the preheat's has an effect, generally we found that too much flux would cause the same issues, altho if your killing you flux too soon with excessive preheat then you'll have trouble at teh wave seperation which lead's to bulbus joints. You should also have a look at your bath, both in term's of the time in the bath but also the temperature you have it at, small changes in temperature have a big effect in the viscosity of the molten solder and again this can be a factor. We looked at the following Level 1 level 2 Level 3 Flux weight Preheat (topside temp priot to wave) Solder temp

and found teh sweet spot there the graph turned up again, sometimes you never get ide of the bulbus joints due to poor design of the PCB but you can usually minimise them. One other thing that we found was obviously some fluxes are better that others for minising this problem, you'll need to play around but also check that whatthe flux manufacture say's their flux can handle in term's of temp is really what it can....sometimes these guys are wrong.....

JOhn

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#2696

Re: Wavesoldering | 24 October, 2000

John makes good points that are in line with those made [in the SMTnet Archives] when trying to solve solder side bridging problems in SOIC and such.

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