cure die attach in vacuum

Curing die attach in a Vacuum

We often get ques­tions about cur­ing in vac­u­um. Sure, it sounds like a great idea on paper but is it real­ly worth it? To make a long sto­ry short, No. If you are inter­est­ed in the long sto­ry, keep reading.

Cur­ing in vac­u­um is a rather unusu­al process, and some­thing that we do not nor­mal­ly recommend.

Three main reasons to avoid vacuum curing:

  1. There is a risk that some of the more volatile parts of the for­mu­la­tion might evap­o­rate before they react & crosslink. As a result, the for­mu­la­tion of the adhe­sive may change in unex­pect­ed & unpre­dictable ways, and will affect the final properties.
  1. Trans­fer­ring heat in a vac­u­um is more dif­fi­cult than in air (or nitro­gen). This pos­es a risk that the parts will not heat at a uni­form rate, or achieve a uni­form tem­per­a­ture. These vari­a­tions will affect the final prop­er­ties of the adhesive.
  1. From a prac­ti­cal point of view, the inside sur­faces of the oven (and vac­u­um sys­tem) would soon become con­t­a­m­i­nat­ed with out­gassed prod­ucts from the adhe­sives (main­ly resins) and would need fre­quent cleaning.

Please bear in mind that adhe­sives can be ful­ly cured in air (or nitro­gen) and then exposed to high lev­els of vac­u­um with no neg­a­tive effects.

As for cur­rent expe­ri­ences, we are not aware of any cus­tomer that uses vac­u­um cur­ing for die attach and sim­i­lar process­es. It has been dis­cussed in the past, but no major cus­tomers have imple­ment­ed it yet and prob­a­bly for good reason.

Reasons to cure in a Vacuum

What is the prob­lem you are try­ing to solve and what would lead you to cure in a vac­u­um any­way? The most com­mon response would be Voids. If you are try­ing to solve your void­ing issues there are bet­ter and eas­i­er steps that you can take to go about it. 

As a start­ing step, we rec­om­mend to inves­ti­gate the root cause. Often opti­mi­sa­tion of dis­pense pat­terns or opti­mi­sa­tion of cur­ing pro­files can help. 

In oth­er sit­u­a­tions, such as cap­il­lary under­fills or die attach films, cur­ing under high pres­sure can help to col­lapse voids pri­or to cure. Pres­sure ovens such as the APT ones that we use in our labs can work great for such operations.

Choosing the correct die attach or underfill material

Anoth­er very impor­tant step is to choose the cor­rect die attach or under­fill for your pack­age. There are epoxy prod­ucts such as the mul­ti­pur­pose LOCTITE ABLESTIK 8361J, the low stress LOCTITE ABLESTIK 8900NCM, the hybrid LOCTITE ABLESTIK 2000 and the high ther­mal, Grade 0 capa­ble LOCTITE ABLESTIK QMI529HT-LV that are famous for their void free prop­er­ties. And we haven’t even touched oth­er chemistries such as cyanate esters like LOCTITE ABLESTIK JM7000 made for her­met­ic packages. 

Are you try­ing to pick the opti­mal mate­r­i­al for your void free bond­line and you don’t know where to start? Our prod­uct cat­e­gories of Die attach pastes, Die attach Films and Under­fills should be your start­ing point. Or you can skip all that and Con­tact us to get a per­son­alised sug­ges­tion for your appli­ca­tion needs.

Void­ing is a blog post of its own. One can write papers upon papers on how you need to store, han­dle, dis­pense and cure the mate­r­i­al to solve this issue so we’ll ded­i­cate one of our upcom­ing blogs on Void­ing and how to elim­i­nate it.

Want to stay on top of the new semi­con­duc­tor pack­ag­ing devel­op­ments, tuto­ri­als and solu­tions? Feel free to subscribe. 

About George Kountardas

George is a Jack of all trades with an unappeasable inquiring mind. Obsessed with new products and technologies, he is always pushing forward for better, faster and more efficient applications. Always learning something new.

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